Okay, I suppose that is a fair enough point.
But are you then saying that how exactly you are supposed to feed these mounts should in no way be a consideration at all? That's really the primary issue I see with so many of the suggestions here. How exactly are you feeding these things?
How realistic do you want your game to be, and how much do you care? There's going to be a spectrum out there - people that want more-or-less-realistic with the addition of magic and the anything goes crowd.
Neither view is right or wrong, it's a choice you need to make with your group.
You are correct that in general, carnivores make really poor mounts because of their upkeep cost. A tiger, for example, takes 10-25 pounds of meat per day. That would be difficult to keep up. Bears are omnivores so they're a little better, but still expensive because they're larger. Of course elephants also have huge upkeep costs and are dangerous creatures yet they were (and still are) used as mounts.
Which means that there might be an elite subgroup of bear cavalry, that is supplemented by ram riders.
In my campaign I had dwarves riding spiders in part because the dwarves could raise giant grubs that the spiders fed on (when they weren't being fed the unfortunate orc here and there). It was also thematically appropriate because the clan was a little suspect, but that's a different issue.
Another issue to consider is the physical build of the creature being ridden. We don't ride wolves for several reasons, but on is that their backs could not support a rider long term. So while I agree goats make a lot of sense for dwarves, they would have to be specially bread to support the weight.