This is just the natural progression of a WW barb, once damage reaches a certain point, you have to move up MP's in order to keep WotB up.
Now my question: is there anyone out there who has too much dps for mp10? As in they kill white mobs too fast so their tornadoes don't get enough ticks in on mobs for the chance at crit creating fury to sustain WotB.
Is this a possible problem WW barbarians start to face as blizzard will revamp legendaries again and continually add better gear to the game (keep the item hunt going)?
It's a weird problem, but it's a foreseeable one with the way the WW barb works.