I want powersets to be on a sliding scale of doing several things.
Blaster powersets should basically all do the same damage. But they can do single target damage, aoe damage, control, and debuff. So powersets should have a mix of these.
It would be fine for blaster powersets to have 5 powers that were essentially the same for all sets - single target attacks of different power but with a different secondary effect. Then the other 4 powers provide the real customization. AoE, control, or whatever.
You could have a set with 4 control powers, 4 aoe powers, a mix, etc. So you can pick a set that has the balance that you want.