Having many abilities has its perks actually. For instance you can compensate average movement with better comprehension of game mechanics and anticipation. I'm thinking of a barb of Fury that moved really well but still struggled when it came to "organising his fight" thus losing to people moving very slowly in comparaison.
But i disagree with the amount of dexterity needed. In PvE it mostly falls down to knowing the tactic, paying attention and being able to press forward and sprinting at the same time. Not to mention that these days for all encounters you have scripts warning you 15 seconds in advance when you'll need to sprint.
I think most heavy "dexterity" issue in this game are based on levelling. When people start the game, they bind things progressively and get use to them and when they arrive at level 80 they are stuck with terrible keybinds they don't have the will to change. Habits die hard...
PvP wise if the sprint revamp made movement much more important than it use to be, before that you really didn't need to have good movement to be decent in PvP it was more about synchronisation with other players outside of 1vs1.
For the record i met two blokes with one hand on AoC. One was actually a pretty good PvP demo in his time, the other only discovered there was combos ingame after 6months though playing only conq and having been level 8O for 4months... so he doesn't count ^^