#full context

TL;DR

WAS JIREN MADE WEAKER?: No. SSBKK Goku, SSBE Vegeta, & Jiren are all in the same realm of power as Gods of Destruction; a realm of power below Angels. However, Jiren is at the top of this realm of power. So, when knowing & applying context from the series, Vegeta's statement about Jiren's power not being so different from their own does in fact make sense.

WAS GOKU DUMBED DOWN?: No. Goku didn't know that Vegeta was meditating because Vegeta has never trained his mind before. He just thought that Vegeta didn't want to train with Broly (which was in fact part of the reason why Vegeta wasn't training with them).

1.) GOKU DOESN'T KNOW VEGETA IS MEDITATING

Many in the fandom have accused DBS: Super Hero of making Goku so dumb that he doesn't know what mental training is. But, that is taken out of context.

When we examine this WITH CONTEXT, we understand that Goku obviously understands training the mind, but since Vegeta doesn't meditate, Goku was wondering what Vegeta was doing. The reason that Goku, Vegeta, & Broly came to Beerus' planet was to test out their current power. But, Broly almost losing control of his power often & that was getting irritating for Goku & he felt like he couldn't get any training done.

Then, a frustrated Goku sees Vegeta sitting around & thinks that Vegeta just doesn't want to spar with them because Broly can't control his power (which is in fact partially the reason why Vegeta didn't train with them).

So, Goku tries to convince Vegeta to come physically train with them & speaks about how there are amazingly strong guys like Jiren, Broly, & Gods of Destruction.

(All of the ones Goku mentioned are in a similar realm of godly power).

Vegeta then tells Goku that he's training & Goku doesn't believe him. THIS scene here has been purposefully & unknowingly taken out of context & caused many fans to misunderstand the scene.

To reiterate a bit, Vegeta never meditated nor trained his mind. Vegeta's main focus was always on beefing up his body. So, Goku mistook Vegeta's inaction as him just sitting around and not wanting to train with them.

GOKU: He always trains body & mind due to his martial arts upbringing on Earth.

VEGETA: Due to the fact that Saiyans take great pride in their physical strength, Vegeta always trained his body. It's unlike Vegeta to train his mind because of his Saiyan upbringing. (Most aliens don't train their minds to get stronger in DB. Earthling martial artists are a rare group who understand this.)

BROLY: He does not have understanding of meditation due to Saiyan upbringing & was only taught by his father to train his body. (There's even a scene where Broly tries to mimic Vegeta after he finds out that Vegeta was training his mind.)

So, when Goku wants to train with Broly & Vegeta, he's thinking from the perspective of two Saiyans who don't do mental training like he does.

2.) JIREN'S STRENGTH

Here's another point of contention in the fandom. What does Vegeta really mean when he states that Jiren's power wasn't so different from their own?

Do you remember how in Battle of Gods, Goku's SSJ3 power was nothing compared to Beerus because Beerus was in a different realm of power? Well, with god ki, Goku & Vegeta have reached a realm of power shared with Gods of Destruction. Jiren is at the top of that realm of power.

So, SSBE Vegeta & SSBKK Goku's power were indeed in the same realm of power as Full Power Jiren. However, power progression at this high of a level is not as rapid as it was before. More power requires even greater control of body, mind, & spirit.

(An example is UI Goku in the DBS anime continuity. Even though Goku's mind & spirit could use Mastered Ultra Instincts power, his body couldn't fully handle the toll of Mastered Ultra Instinct's limit-breaking power.)

Vegeta thinks about what it was about Jiren that allowed him to be even stronger. Not only was Jiren physically strong, but he was mentally strong as well. Due to being able to think clearly & conserve his energy, Jiren could take on 2 opponents that were relatively "close" to his own power. A disciplined & focused mind is also able to draw out more strength.

Freeza's path to power is an example that is a bit similar to Vegeta & Jiren. Freeza even realized that mental training would improve his Golden Freeza form while he was in his own personal Hell.

Goku & Vegeta were using their stamina carelessly in the ToP & their attacks were not focused like Jiren's attacks. Goku's Ultra Instinct Omen was closer in power to Full Power Jiren due to the focus that Goku had, but even then, Jiren was still more masterful of his own power. And being in control of your power is very important in Dragon Ball. BUT... Super Full Power Jiren was leagues above both Goku & Vegeta's SSB powers.

It seems that Vegeta is not referring to Jiren's awakened strength when Super Full Power Jiren fought MUI Goku. Vegeta's referring to when he & Goku fought Full Power Jiren together in their SSBE & SSBKK forms.

Vegeta has come to the conclusion that Jiren's strength comes from unity of mind, body, & spirit. Which of those 3 has Vegeta always lacked? And that's why Vegeta's now training his mind.

Vegeta mentions how Jiren was fully relaxed until he delivered an unpredictable attack in an instance. Unlike Vegeta's wild fighting style that ends up wasting all of his energy in an attempt to overpower his opponent, Jiren's fighting style conserves stamina while also making full use of his overwhelming strength.

Jiren cultivated his ki through meditation for much of the ToP as he conserved & replenished his ki after a battle.

Jiren often calmly walked towards his opponents, conserving his energy.

Jiren quickly delivered powerful strikes when when he saw openings in his opponent's defenses. (Goku begins to move in similar ways with UI.)

Simply put, Jiren had better control of his ki than Goku, Vegeta, & Gods of Destruction. That masterful level of control allowed Jiren to become stronger & stronger.

And this part is really interesting. Vegeta says that Jiren probably achieved this kind of power by "INSTINCT."

What has Whis been trying to teach Goku & Vegeta all of this time?

Don't overthink, conserve your stamina by relaxing when necessary & not making unnecessary movements; the principles needed to achieve Ultra instinct/Migatte no Gokui.

Jiren: He has a focused mind that allows the body to move instinctively & conserve energy so that he can dodge, block, & attack when necessary.

Goku (UI): His body instinctively moves without thinking, and conserves energy by dodging, blocking, & attacking when necessary.

Vegeta has finally discovered why it's so difficult for him to achieve a power like Ultra Instinct. But, because he's unable to do so by instinct, Vegeta will now start training his mind in order to reap similar results as Jiren.

(Jiren never meditated in the DBS manga continuity. He only did so in the DBS anime continuity. So, since it's been confirmed that the movies take place in the DBS anime continuity, Vegeta is following Jiren's path to power & he begins to train his mind.)

(The DBS manga continuity has Ultra Ego, but the anime continuity does not imply that Vegeta has such power. Ultra Ego seems to be a manga exclusive power just like Perfected Super Saiyan Blue. At least for now.)

3.) WHIS' STATEMENTS

Here's another scene fans have taken out of context (wether purposefully or unknowingly).

What's happening here is this...

Whis is impressed that Vegeta finally figured this out since the principles of Ultra Instinct were difficult for Vegeta to grasp for almost 5 years.

Whis reminds Vegeta & Goku that training is not to simply beef up the body (as Vegeta's mindset had been before).

Goku nods in agreement & says "Yeah." This reveals that Goku understands what Whis is talking about.

Whis teases that it took Vegeta a long time to catch on to what he's been trying to teach them about Ultra Instinct.

Whis then says that this has not FULLY clicked for Goku. Meaning Goku has more understanding of this than Vegeta does (which is why Goku agreed a moment earlier) but, he still requires more training in order to fully master Ultra Instinct.

Because Goku always trained his mind, he understands Ultra Instinct's principles better than Vegeta does. This is why Goku & Vegeta broke through their shells in different ways. Goku awakened to Ultra Instinct Omen while Vegeta evolved SSB to Super Saiyan Blue Evolution. And in a way, SSBE is sort of Vegeta's own version of "Ultra Instinct Omen." What do I mean by that?

The eyes of SSBE are similar to Goku's UI Omen & it's also limit-breaking power. But just like how Omen isn't the full understanding of Ultra Instinct, SSBE isn't the full understanding of it's different route of power. Jiren became strong from absolute determination & mastery of his body & mind. A path of power through determination is what Vegeta has always been on. Determination is how Vegeta pushed SSB's limits & evolved it. The next step of evolution for Vegeta is for him to gain a mind similar to Jiren & find a power that can rival Ultra Instinct just as Jiren did in the anime.

So, unlike what many online have said about these scenes, FULL CONTEXT shows us that Goku was not being dumbed down. Goku just never saw Vegeta meditate. Meditation is something more in line with the martial arts mindset.

4.) EVOLUTION OF VEGETA'S FIGHTING STYLE

Whis decides that the three Saiyans should have a sparring match to test out what they've learned. Vegeta refuses to spar with Broly who still cannot control his power. So, Whis has Broly observe Goku & Vegeta's sparring match.

(Remember when I mentioned earlier that part of the reason why Vegeta didn't want to train was because of Broly? This is why Goku didn't immediately realize that Vegeta was doing mental training.)

Vegeta's fighting style prior to this movie was to go all out & attacking without focus, but that's begining to change for the better. Goku's style is to adapt to his opponent's fighting style, but that can also use a lot of energy at times.

Beerus even takes note that Vegeta's movements are now slightly different.

Vegeta (reactive) waited for openings.

Goku (proactive) created openings.

Similar ideology, different methods.

Goku struggled to attack without overthinking when using UI Omen & he was more reactive than proactive in this form. But, while in Mastered UI, Goku was more proactive as he dodged AND attacked without thinking.

Perhaps the anime continuity could give us a "Super Full Power Vegeta" that has a flaming red aura like Jiren?

Goku: Silver hair & eyes. A blue/purple aura.

Vegeta: Silver hair & eyes. A red/purple aura.

Or maybe something else entirely.

CONCLUSION...

When scenes & dialogue are purposely taken out of context, things are easily misunderstood. This can poison the well & get many in the fandom to hate the movie based off of limited info without even watching the film for themselves. And when some fans do watch the film, they could have the wrong perspective of events in the film due to context being withheld which resulted in misunderstandings.