Druids don't need a power-down?
IMHO, it was a bad idea to combine a primary caster with a strong combat capability in the way that the druid works out, which is, specifically, casting + combat capability rather than casting OR combat capability. The fact that the master of many forms (shifter) doesn't get a spell progression is, IMHO, pretty good indication that having shapechanging capability is plenty powerful without needing massive magical ability. the PHB2 variant seems to support that, and I think it's strong enough.