I agree with this, to me a better approach than the blanket nerf in reaper would be caps along the lines of Jump skill. The problem with casters is the top end, not every build and every class. An easy way to get at that is to cap key damage components by level, it does require a bit more thought.
This can also be done with other key values like Melee Power, Range Power, Doublestrike, Doubleshot. There are in the end only 10 or so key values for balancing DPS. Cap those and you can ignore all the build combinations and complexity.
For example at level 32 it might look something like
(Max cap for values, anything over that amount does nothing ala Jump cap)
Level 32
Spell Power - 800
Spell Critical Chance - 50%
Spell Critical Damage - 75%
Helpless Damage - 40%
This also gives great tool to balance by just tweaking the numbers. You probably only need a few of these at key levels:
Level 5 (and under 1-5)
<Insert Caps>
Level 10 (and under 6 -10)
<Insert Caps>
Level 19 (and under 11 - 19)
<Insert Caps>
Level 28 (and under 20 - 28)
<Insert Caps>
Level 32 (and under 29 - 32)
Spell Power - 800
Spell Critical Chance - 50%
Spell Critical Damage - 75%
Helpless Damage - 40%