I agree with OP that Yuri had little to no character development, but in Vesperia’s case, I think it’s actually better that he didn’t have development. I think so because to me, it feels more like Yuri is the sort of character that makes others shine. I feel like he was responsible for Estelle’s, Flynn’s, Karol’s character development and so on. I can’t help but wonder that had Yuri been given more attention, would those characters shine as much as they did? Yuri casts light upon them precisely because he doesn’t have any major importance despite being the main character and that’s something that I really appreciate about him. If we simplified Yuri’s role in Vesperia, he doesn’t serve any other major importance other than being the link that maintains the other characters together. In fact, Yuri seems to enjoy his lack of attention - hence why he didn’t care when Flynn got the credits all the things he did.
Yuri never decided things for other, instead he gave them the option, made them think for themselves, and once they decided upon something, he’d simply guide them through their path - like when Estelle decides by herself that she wants to continue the journey with them or when Karol decides to start his own guild. Yuri didn’t ask for Estelle to come, he didn’t influence her decision. He never tried to be Brave Vesperia’s leader, he always supported Karol’s idea from the sidelines and helped them both when they needed him. (btw, I’m only talking about Flynn, Estelle and Karol, but this also extends to Rita, Raven and Judith as well)
Usually in RPG’s the main characters hog all attention to their own development (ie: Symphonia and Abyss), so Vesperia brought something new in this aspect and I like it just like that.
It’s not that I disagree with this confession, on the contrary, I totally agree that Yuri didn’t develop much, but I’m not so sure about whether it would’ve been better for him to actually grow or not. It’s something I suppose we’ll never know for sure.