I think this is the reason why stan culture is so bad in this game. All three characters are heavily flawed but the game outright refuses to acknowledge this when you go into each route. The only exception is maybe Dimitri, although, the game cures his mental instability in a few poorly-executed scenes, so I consider that as a whitewash. I find it pretty annoying when I see someone post an "EDELGARD/DIMITRI DID NOTHING WRONG!" post on Reddit.
I know some of the people here like Rhea and all, but I find her support with Byleth a bit creepy. Sure, with context it makes sense why Rhea is behaving this way, but it doesn't really seem like that when I put my feet in Byleth's shoes. I like Rhea, but her support just isn't for me.
I meme a bout stanning Edelgard when chatting up my Fire Emblem Bros, but I really am kind of bitter about how one-dimensional the interactions between the main characters are in each of the routes especially considering how well everything else is written. I hate that you can never give Edelgard a chance to challenge her stance ideologically without kissing up to the empire given her backstory and interactions/opinions of the other Lords in the game are much, much more charitable even post time-skip compared to Claude's dismissal of pretty much everyone in his route and Dimitri's everything. (To an extent, anyways) I hate that Dimitri's route is basically Sasuke Uchiha's entire character arc in Naruto sans the part where his fuck-ups truly come back to haunt him and he wins in the end despite
clearly being the least mentally sound Lord. And I especially hate the fucking tease in Claude's route regarding his distrust of Rhea and the Church, his (too few) scenes where he clearly intellectually bounces off of Edelgard, and the empty promise that is exploring the rampant opportunistic attitudes present in Fodlan that could be argued as the true vice in the story that causes the bulk of the suffering. (Something Claude himself can arguably be called as just as being guilty of.)
Rhea's got a lot going for her that certainly makes her stand out as a character and a influence on the story, and how twisted a lot of who she is admittedly was probably intentional, but I found myself wanting to fucking axe her in every route because I just can't stand someone so conniving and delusional. She created a society where she got to stay at the top allowing herself to do fuck all while still feeling entitled to everyone's loyalty yet when she oversteps boundaries I have to push and shove to get any sort of catharsis or answer out of her. Say what you will about Jeralt, I simply cannot be more open to her character when he spends the entire story rightfully distrustful of her. Couple that with her blatantly lying about him after his death and never really getting called out on her manipulative behaviors makes her an incredibly unpleasant presence on the story that you rarely get a break from considering the other Lords don't do a good job at all comparing to her. (From a story-telling perspective, not a character one.) She's decently well-written, yes, but I still don't like her.
There's a lot that you can work with regarding 3 Houses' plot. I like what I have, but it only disappointing me that Ashen Wolves didn't do more for the story simply because they don't want to overwrite the choices the player can make.
Intsys, please. I can just ignore DLC if I wanted a pure Golden Deer run. Having post-release content have new interpretations of the story is not something I imagine most players will care about, especially if you avoid the "Golden Ending" pitfalls that Revelations was years prior.