Speaking as a fan of Kibayashi's works, I would say that his works are primarily detective mysteries. You can probably already tell how different that would be from a fantasy war game.
While Kibayashi has quite a bit of experience with fantasy, I've never read a story that he has written with so many characters. It was probably changed to fit the general tone of Fire Emblem games.
I also believe there is a second writer for If. It's quite possible that their ideas clashed and If is the result of a compromise between the two.
Edit: I almost forgot to mention. As someone who has played both Nohr and Hoshido, in the middle of IK, it's best to play the game yourself first with decent standards, then form your own opinion. What I'm seeing across the internet are people with way too high expectations.
I personally love it despite a few flaws. I like it more than Awakening. I recommend avoiding most things like forums until you've had a good look at the game yourself. I'm pretty certain quite a few people here are hating it without having played it themselves, I think there are people who've uploaded ongoing translated playthroughs on YouTube, if you can't wait for the English release date.