Re: Rean. He isn't perfect. The game hardly treats him as so. He is hard-working, humble (to a fault) and loyal and that gives him some clout in the eyes of many characters in the game, but he also has his faults (like that being too humble part, which is pointed out in the game numerous times). He THINKS he knows best when it comes to stuff about him personally but a lot of the time life would have been easier for him if he had some outside perspective. He pushes himself a bit too far alone without asking for any help, especially with that personal stuff. While he gets along with all kinds of people & can have some fairly deep conversations with them without any prejudices clouding his judgment, he does keep his distance to most people.
He's a good leader for the group but mostly just in comparison to most others in the class. Alisa is too impulsive & hot-headed, Elliot is too timid, Laura is a bit too much of a schooled aristocrat('s daughter) even if she's not snobby, Machias is an ass & too involved with the divide between the noble & common folk, Jusis is a bit too who-gives-a-fuck, Emma isn't one to put herself too much in the spotlight and Fie is too much of an outsider and not all that socially adept. Gaius could actually be a decent leader but I have a feeling he's a bit too much of a hippie to really want that top spot, unless forced upon him by chance.
He does get some development in those areas in the first Cold Steel (except the goofy grandiose motivational speech thing that is just encouraged by the class by the end, though in a joking "oh boy, here he goes again. Well, let it out already" manner), though I'd say the same things are a bit of a problem for his character arc that are a problem for all characters & the story as a whole. The cast & country is just so big + this is basically just the introductory first half of a game divided into two and as such it leaves a lot of character arcs without much resolution.