My experience is generally that fighters and their ilk are more popular and more powerful at all levels, and that casters provide specialized expertise, plot device opportunities, and support the fighters.
At high levels, magic is not as effective as it reads. Anything that a character does is subject to massive scrutiny. Sure they can rain death and destruction on a few kobolds or human commoners if they want, but if they try anything stupid, someone more powerful than them is bound to notice. Almost every significant enemy has SR or some defense against magic, and at high levels, everyone has a ton of save-boostng items and rarely fails a save. Some common-sense DMing eliminates a few overpowered spells and combos, but for the post part, casters focus on something like healing or area damage, and chip in with a lot of out-of-combat divinations and the like.
Fighters, conversely, get all the powerful items, and have ridiculously powerful weapons. They can reliably ovecome any DR, and are likely to hit any enemy, and thus, where casters are often dumbfounded, fighters can deal damage reliably every turn of combat. A typical battle is decided by who supports their tank the best. Martial characters also tend to accumulate respect and political power, where casters tend to be separated from society.
I've been playing for over ten years now, with quite a few different people, several times at high levels and even in epic a few times, and I'm convinced this "god wizard" business is a myth. Well, not that it doesn't happen, but that it isn't a natural consequence of the rules. If anything, casters hit a sweet spot a little after 10th level (Heal, Disintegrate, Teleport, etc.), but fighters tend to reassert themselves later. There's room for improvement in limiting the sheer complexity of high-level casters and improving the breadth of options for fighters and rogues, but there's no need to reinvent the wheel.