I can't see these mounts completely eclipsing Chocobos in any way so I don't see what the problem is. Especially if there's enough of a diversity of different types you wouldn't see people all riding around on the same thing, as some seem to have a problem with. Honestly you'll probably see them around a lot for a week or so, then everyone will go back to riding Chocobos outside of showing off their different mounts.

To me, it makes less sense that we can't ride them. There's no lore saying we can't throw a saddle on monsters that are big enough and use them as mounts. It doesn't conflict with the current story or lore at all. I honestly don't see what the problem is. I don't see why we can't have Chocobos AND other things, I mean aside from people wanting to control what others do because it "annoys" them.

Also since they've pretty much finished the system and put all that money/work into it, it's going to come whether you all like it or not.