This whole thing bugs me as well considering they CLAIM the game had inspiration form FE4. Like... where? The bloodlines and the mole people and that's it? Bloodlines are in other FE games but not in terms of special abilities for the most part, so that's where the inspiration feels strongest, but even then, that's part of the problem with this game.
The reason Naga stopped getting involved with humans was because they got power from dragon blood but used that power to wage war on each other again and again. While I'd argue her lack of interference was forced and imposed upon all dragons (i.e. she tried to control them all and basically didn't allow, by law iirc, that dragons were no longer allowed to interact with humans, which plenty dragons said fuck you to), Rhea... didn't do this. She didn't force others of her tribe to stop interacting with humans and continued to herself, but Naga's way of doing things wasn't a choice. When Seteth chose to stop interacting with humans for as long as he did, it was a choice that Rhea left him alone to make.
Then when it comes to humans waging war on each other again and again, Rhea didn't just abandon the good humans who weren't doing anything wrong. She didn't see a few bad apples and go "wow all of humanity sucks, I'm going to leave them for dead, one and all". Some people who have followed me long enough know I have a Big Fat Grudge against Naga and hate her pre-Marth time (i.e. Jugdral's time), and it's because she ultimately decided all humans weren't worth saving because some sucked.
Rhea on the other hand fears extinction of her kind, rightfully so, and yet still can't find it in her to abandon humans. She helps with taking down bad humans (I'm sorry buddy (not really though lol) but if you think someone looting a church isn't bad, you are bad). She only gets involved, however, when the issue is either directed at the Church she lives in (i.e. her people are put in any kind of danger), or her help is directly requested (ex. the Kingdom needing help, or even Edelgard in SB asking for her assistance to deal with Thales).
The game writes Rhea out to be this horrendous person who is a "world" controlling tyrant (because ah yes, she's forcing Morfis to do her bidding. Were you not aware?! Poor Brigid has her will imposed upon them at all times! Sreng is forced to comply with the Church!!! Sure can't believe Rhea has such an influence on the whole world, huh Edelgard?). They let the narrative write her off as having a hand in all the politics, even though like... the Alliance doesn't even really know her. Or care to. She doesn't interfere with them and they don't interfere with her. She went to visit Goneril once that we know of, probably saw that they were taking in child slaves, was disgusted, took the one she saw, and noped right out of there and never wanted to come back.
Then with Faerghus' politics, even though she's got the best relationship with Faerghus, she's not even involved in those politics. If she was, guess what? Dimitri would've been crowned king at her request. He could have gone to her and they could've both said well fuck the idea that you have to be of legal age to take the throne. Yes, I believe she cares for Faerghus' people enough that she's willing to help if asked, but Faerghus deals with its own politics. Rhea doesn't assist unless asked. Have they asked her for help with Sreng? Nope. Did Lambert ask for her help in his plans with Duscur and Sreng? Nope.
And of course, if you say the people of Faerghus were suffering because of Rufus' lack of proper reign and Rhea didn't help, she's demonized for that... but if she did help, she'd be accused of trying to control Faerghus, so either way, she can't win... and the narrative does do this to her and the fandom already hated her for being of a church, so it just took over the majority's perception of her. She's damned if she does or doesn't and her very existence is basically a crime to the fandom and the narrative both.
Adrestia has a slew of political issues, and Rhea had no hand in it. Yeah, the whole Crests thing is a problem in Adrestia (and only Adrestia, don't even get me started on that topic), but Rhea doesn't control what the power structure is like there (or anywhere). If they fight over that shit, it's not because she did anything to make them. She leaves them to deal with their own political strife unless asked for help (again, SB), just like she does with the other Fodlan lands.
We know Crests aren't even her fault so I'm not gonna even bother getting into that.
The sad part is that the narrative paints Rhea as being at fault for the Agarthans slaughtering her brethren and using their blood and bones for power. It then uses her trauma to label her a monster. All Rhea has ever done with humanity is help them if they asked her for help, and what did her help entail? The help of, wouldn't you know it, other humans. People like Catherine and Gilbert were her go-to people for support when asked for it. She would send her personal knights, humans, to help other humans.
Humanity (including Thales and co) are shown to do horrific things, but Rhea is blamed for everything? All the woes of Fodlan? Rhea is at fault for Metodey being a scumbag? For Erwin getting Claude's uncle killed? For Gregoire using his daughter to be a trophy wife while evidently being such a terrible person to her that she's terrified of him? For Rufus refusing to even actually rule and letting Faerghus nearly fall to ruin, leaving the capital in a terrible state? And if you count Hopes' background information, he tried to have Dimitri assassinated multiple times, and it wasn't so subtle that it went unnoticed. But well, I guess that's Rhea's fault too.
Anyway, point being, humans do human things and Rhea magically gets blamed for it. Yet, the game they took inspiration from had humans doing the exact same bullshit, fighting each other and trying to decide who should have this that and the other in regard to power, and it was... a dragon who helped the good humans get through it and survive. Who had to help them because the other humans got so out of control and barbaric on their own, with dragons not involved in their lives at all.
He helps them, doesn't tell them his identity, is only found out by the main character, and takes his leave at the end of the game. He helped them and left them to it and is portrayed in the game in a positive light overall for having helped the good people survive against the humans who were warring against them.
Again, that is the game Houses took inspiration from. Hence why, again, I can only see the bloodline thing being their sole inspiration overall, because the way they wrote Rhea would make me think they looked at FE4 and went "hmmm humans bad in both games... but how about in this game, we blame everything humanity does literally ever on the dragon!", even though like... humans would war with or without dragon power. If... you know... our own reality is... any... indicator...