I agree with you conceptually, but that's not how 3.5 was designed. The underlying math assumes you're getting magic weapons, armor, stat boosting items, and so on. (The easiest place to see that is AC-- attack bonuses go up with level, AC is roughly static without items). The "classes can't contribute without items" thing is probably accidental, but the need for "big six" magic items is very real. You really can't cut them out of 3.5 without some sort of replacement.