If you want to talk about caster supremacy, you need to pin down the exact problem that makes martials so second-rate first.
The main problem with full casters is twofold.
Firstly, they have options (i.e. spells) that non-casters simply cannot counter or deal with. You can be as strong as you like, as sneaky as you like or as tough as you like, it does not protect you from an enemy caster turning you into a duck (baleful polymorph), mind controlling you (dominate person, geas), or simply taking all those advantages away from you by taking you down a few levels (enervation)
Secondly, non-casters don't bring a lot to the table that casters cannot do by themselves with their spells. Sure, the fighter and barbarian are pretty tough and good at combat, keeping the men with pointy metal things away from the casters, but casters can make melee fighters by themselves. The druid is the obvious example here, but wizards and sorceres can always spend a few slots on summon monster or planar ally and throw some meatshields into the fray. As for rogues, what point is there to being good at sneaking if the caster can just make himself invisible, teleport where he wants to go and use illusions to distract trublesome guards- while still able to do all the other stuff here.
The counterpoint to all of this is that casters use a finite resource to cast spells (spell slots, and sometimes material components), while martials can do their thing all day long. And that is true in concept, but in practice the resources are not that limited, and especially at higher levels (where the spells themselves get REALLY broken) casters have enough slots to cast all day every day, especially when you get to feats like versatile spellcaster. Also, people will mention by now that casters only have access to so many spells, but for everyone but the sorcerer (and the favourite soul), and very specialised casters (warmages, beguilers), that is simply not true.