They could introduce some weaker versions of abilities at lower levels so that the number of abilities you gain between... say, 30 to 100 doesn't increase very much. I dunno if people will find that very interesting, though...but I'm of the opinion that we have far too many buttons as it is and gameplay can be made more engaging in other ways instead of just memorizing a string of buttons to press every 1 or 2 minutes.

Thing is about scaling down is that relative damage isn't the only thing that improves as you level up. A level 100 tank has far better survivability than a low level one due to having better and more defensive cooldowns and self-healing. People already complain about healing being pretty boring due to lack of DPS buttons to press and tanks having too much self-healing, now imagine running a low level dungeon with a warrior with Bloodwhetting, Nascent Flash, and Shake it Off. That's not going to be a fun experience for a new player if you never have to press a single heal because your tank can handle everything in a dungeon that wasn't designed that way.