I see where you are going. You have acknowledged the difficulty in meshing with mmorpg. Very good.
now, a LOT of the stuff is in game. Just not lumped together in one powerset. For instance, you can get your toon to move pretty fast with buffs from other sets. AND you can “look” like you are attacking fast with something like Shadow Maul. Now, if you want all the effects of shadow maul, but cut the long animation time, that is where problems start. You cant rebalance a power. And if the Devs did ALL Dark melee users will hate them, having struggled with this beast forever. But the speed self buff would need to be in the defense set, and of course the attacks in the attack set. So, two new power sets to make this