Perhaps, but the CM Wiz comparison is still sound, for nothing else to demonstrate that while you can earn more experience for paragon leveling on higher MPs, we, as Witch Doctor's, have to clear fast enough that the experience bonuses outpace the reduced clearing time. Many other classes can outpace this curve much better than we can. Thereby, its not a long-reaching assumption that for most WDs, playing on a lower monster power, for paragon farming or drops, is the correct choice.
I can easily clear out MP10, but its slow enough that it isn't worth the paragon leveling. If we're talking about gear drops, demonic essences, or key farming, that's an entirely different matter, and highly subjective. But, if we're discussing experience for paragon leveling, it can be clear cut. Simply gauge what experience you can earn after an hour on multiple monster power settings.
Just because you can run MP10, doesn't mean you can do it efficiently. Can it be more enjoyable? Sure, but that has nothing to do with efficiency.
Edit: Darn typos.
Edited by GamerObscura#1236 on 2/25/2013 7:13 AM PST