A storm of any kind is probably an overreaction, but why wouldn't taking advantage of the mouse have been a good idea? Differences in content between versions would be a poor decision, but diminishing the UI for one version to accommodate shortcomings in others seems strange.
It looks nice, though, well set out etc. hopefully we can expand but if not, well, there are worse things in this world.
Because I don't believe it has anything to do with the UI, though that's how it's presented. I think it was a gameplay choice. If they had wanted to do it like before (nad believe me, I played on console for all games so far and had no problem using radial menu to use abilities, which I cannot now), they would have. They chose to limit it to 8 at a time.
We do know they can be switched while in the field, but not if we can switch during a fight.
About Amount of Abilities some are commenting on:
Well, I wouldn't be surprised if that 200 count included all Specializations (you can only pick 1) as well as passives (there are lots and they dont' take up slots), and you also have upgrades. I'm sure we'll still have more than 8, but probably not as many as you might think.