I binge watched all of Steven Universe with one of my best friends, and I now have an opinion on how The Diamonds were handled
While it's really controversial, given we know that the series got shortened I think the Diamonds' reformation was handled as well as it could've been, and was somewhat believable imo, and the biggest key is considering them reformed and not outright redeemed.
For one thing, the Diamonds' actions all stem from White being a genuinely delusional person, who believes herself to be perfect, and that the further others are from her the more imperfect they are. When these narcissistic ideas were disproved by Steven, White went much too far in the opposite direction by letting others possess her instead, which are not the actions of a mentally well person to put it lightly. You get the sense she represses her feelings as much as Steven did, before and after being reformed.
Yellow and Blue are reformed by basically the same thing; realizing their actions greatly hurt Pink and their revelations expanding from there to realizing that their actions weren't really for the "greater good" at all, realizing that the way they think isn't the only way one can think.
Blue, like White, went too far in the opposite direction, which does make sense. She's the most emotional of the diamonds, so her solution to her past is mental. She thinks that she's doing something that makes up for her past because she can't imagine why someone wouldn't want to be happy and, like before, she struggles to understand why someone wouldn't think like her.
I'd argue that Yellow is the only one who genuinely took steps to redeem herself, reconstructing shattered gems by hand. And I think that makes sense. She tries to act on logic the most of the diamonds, and not only did she realize she was hurting Pink, but she actively hurt Blue and realized not long after. She didn't just realize the consequences of her actions after the fact, she saw them firsthand. So instead of just inverting how she previously acted, she actively made steps to improve and undo what she previously did.
Another thing I like is that they didn't improve at the drop of a hat. They still do look down upon non-Gems, they mostly just respect Gems more, and mostly try to be better because of their grief for Pink. All three of them are huge messes, Yellow improved the most because she's the least of a mess.
It'd be better if they were given more time for their development, but I'd say what we have isn't outright bad or series ruining (but that might be because I binged the series instead of watching it weekly as was originally intended)
