Gonna disagree with this one. A Druid has almost as many ways to simply clog up the field as a Wizzie does. Yeah, the lack of things like Solid Fog hurts, but if you look hard enough (hint: Frostburn is fantastic, but even just the PHB and SpC are wonderful), there's no shortage of spells that can seriously get in your enemies' faces and keep them where you want them. (Wall of Thorns, anyone?)