My opinion probably doesn't matter too much, since I haven't played either RD or FEF:C (Still working on Birthright because I take my dear sweet time, but I just had to chip in), but here's what I've got here. (I should point out, I'm not saying who's better, because I wouldn't know, since I haven't played either game)
First of all, it was established on page 2 by OP that information about Corrin gotten from other sources besides the conquest story WAS valid information, so there's one piece that people are way overlooking. Siblings were NOT the only reason Corrin had to pick Nohr. Corrin is more in general very attached to Nohr. you learn that from Azura supports in Birthright. You may think that's a little bit of an obtuse source (also, my Corrin is female, if that makes any difference. it changes a lot of dialogue, i'm not sure if it changes supports), but it's less obtuse than Hidden Truths or subtle implications in Revelations, so meh.
Second, I may be kind of the outlier here, but I think Corrin's actually fairly well written. Admittedly, the whole "Coddling by all of the major characters on both sides" is annoying, but i DID say CORRIN was fairly well-written, not the other characters...or the story in general. One thing to note is that the game is not subtle about the fact that Corrin is an idiot and none of their decisions are likely to be good ones. They are sheltered, naive, overly trusting, and not particularly a hero. Yes, the sword chose them, but that doesn't mean they're a hero, that means they're the one that'll save the world. They are portrayed as a hero because the story is played through their eyes, and everyone naturally views themselves as the protagonist of their story. Corrin is delusional, and I feel that Fates actually does a pretty good job portraying that. Corrin is an idiot, was clearly intended to be an idiot, and they very obviously wanted YOU to know it. Corrin is not a stand-in for you, they are a protagonist that you design. Unusual, but it happens.
Anyway, that's my two cents. Not sure it means anything, but there it is.
