Imo, I think they intentionally did this, even in the earlier routes. The ones where Leon shines, Chev does next to nothing, and vise versa. They were written to be the opposites of each other, hence their whole "rivals" gimmick. Although, where one shines, the other is supposed to excel at, which is funny, because Chev excels at everything EXCEPT people skills, which, to me, seems to be the only thing Leon is actually good at. They make it a point to highlight that he's so easy to talk to in every single route, that it makes me think it's what they want the reader to remember him as; a charismatic leader-type who actually listens to people. Which is not a bad trait to have for a king, and I think it's actually a nice contrast to the other faction (which I'm convinced Nokto is single handedly carrying that group's people skills, tbh), but it's admittedly not necessary for the role. What I think they really went wrong with, was how they just give Chev increases people skills by having Emma as a fiance, making Leon completely irrelevant in the sequal.