Though as an aside, I think the Shapeshift Druid only drops to T2 really, its still a fullcaster with a rage-equivalent combat mode.
Being a full caster doesn't merit T2 status. Just ask the Warmage, Beguiler, and Dread Necromancer. In fact, the Dread Necromancer is practically designed to smash campaigns via undead minions, even though the amount of power it can dish out in a short period of time is limited.
In any case, the Druid's spell list is basically more varied than those of the Warmage, Beguiler, and Dread Necromancer, and not substantially more powerful. Sure, druids still get Shapechange, but DN's get Planar Binding, so just having one offender apparently isn't enough. Sure, Druids get the Bite of X spells, but those buffs do not play nicely at all with the Shapeshifting ability. In fact, you'd be hard pressed to find more than one or two spells that would make GOD go
in those mid-upper levels, even with Spell Compendium. They're all very situational.
Also, Druids are losing a very, VERY strong class feature in that animal companion when using the Shapeshift variant. A PHB Druid is basically bringing two characters to the table, especially at low levels, and has a lot of solid buffs that generally only affect their animal companion or summons, not other party members. As a result, the Shapeshift Druid not only has weaker action economy, but also finds some of the Druid's better spells less appealing because there probably won't be any legal targets for them.