To OP: Absolutely not. I'm fine with mounts being mostly cosmetic, and being able to just go anywhere with whatever your favorite one is. It'd be an enormous annoyance to be forced to use specific ones, especially ones you need to grind rep for. Frankly, I'd start to despise those mounts rather than like them more. If anything, I'd want more mounts to be functional as Companions, especially the ones that already have attack animations finished (drake, elbst, etc).