I haven't been following too closely on Gaim; I know that Gen Urobuchi is the head writer, and I have my reservations on him, but the idea of a Seto Kaiba rider does sound like a lot of fun.

That would have helped, but then again Gai Ikari got a lot of the same hate and he was an active 6th ranger; fandom just really doesn't like this sort of character, the kind that reminds them they're watching a kid's show. As for the emotional center, I don't think I would say there was a singular center, I think there was a pretty involved network of support for the team.

Good for her; I didn't really keep track of who wrote which episodes, but I imagine I could check the Kamen Rider Wikia to find out who wrote which ones.