Keefe the Thief
Hero
There is no boundary-pushing required for casters to dominate mid- to high-level 3.5 gameplay.
In fact, boundary pushing is required for non-spellcasting classes to have the same level of impact on the game itself at these levels. Without boundary-pushing, those classes are left in the dust be even mediocre spellcasters.
God, you reminded me of my Eberron game: the druid stopped calling his animal companion and using shapechange after a couple of sessions because he was embarrased to constantly outdamage the melee guys.