Sorcerer -> Low T1
Explaination: Choosing the right spells (Calling Creatures/polymorphing/Shapechange etc) the Sorcerer can have a vast amound of versatility without sacrificing any Power. in a scenario were Dragon Magazine is an allowed source the item "knowstone" functions for a Sorcerer as a Scroll does for a Wizard. Runestaves can also give access to multiple other spells. Finally the prestige class "Mage of the Arcane Order" can give a Sorcerer the same versatility as a Wizard. Finally some spells give a great bonus to the Sorcerer over the Wizard (Arcane Spellsurge) wile others exclusive to the Sorcerer can give amazing combos between spells (Arcane Fussion and it's Greater Version).
Because some optimisation (not to mention Dragon Magazine) is required to that end (as opposed to regular progression) i can see why it's considered T2. i don't want to oppen an old can of worms by this post either. Just wanted to share my oppinion that a well built Sorcerer deserves Tier 1.