You can't just plug different stories into each other, because they all have different notions of the possible.
A long time ago, D&D reached the point where it needed to decide whether it was to be an Arabian Nights universe of superpowered magic, with every player character a caster of some kind, or a Conan-and-Tolkien universe of brave heroes riding around on horseback, shooting bows, etc... perhaps accompanied by the occasional bone-casting, storm-calling, and even fire-throwing wizard, who cannot fly, talk to the gods, create universes, or bend time... because magic has its limits, too.
And D&D refused to make that decision.
You think D&D is bad on that deparment? Then Warhammer 40K would like a talk with you. It's a setting where you can perfectly expect powered armored mutants with explosive machine guns and space ships to face with pre-historic neandertals with wooden spears. Where the spanish inquisition with killer nuns faces drug-crazed space elves. Where WW I armies roll out against orcks. Where human infantry may as well be riding regular horses, hover bikes or segways. Where undead robots face against daemons. And either of those battles can go either way.
And no matter how nonsensical that setting is, no matter how unbalanced the rules are to the point some choices are never taken and others are autopicks, 40K is still extremely popular because lots of people precisely love that kind of crazy mash-up.
Warhammer 40k is a different beast altogether... the difference being that it's a wargame, and fluff is just that, fluff wrapped around some stats. If doesn't matter if my unit is riding horses or jetcycles in a wargame, the only thing that matters is that stats.
But god-magic in a RPG is something else again, because RPGs don't have a sharp line between fluff and mechanics. If I can fly, or teleport, that's not just X scale inches of move that ignores terrain. That's the power to break certain types of plots... and it's a power that is available to some character archetypes and not others.
One of the major appeals of RPGs is that it's Halloween with a story. You can be who you want to be, and go have adventures as that person. But D&D supplies a bunch of different character templates based on fiction, and balanced, not with each other, but with their fictional counterparts.
This is why we have tiers. Because Tiers are largely a function of the stories that generate them. Fighters are in the Conan tier. Wizards are in the Rand al'Thor tier. You can't make them work together because the
stories they are from don't work together.
That's why people don't like ToB, for example. Not because it's overpowered, but because it takes Conan out of the Conan story, and forces them to play the Stone Monkey instead. Now, playing the Stone Monkey is a fine thing, but it's a fine thing in a Stone Monkey story. People who play fighters want to play Conan in Hyperboria.
Problem is, they are sitting at the same table with someone who wants to play Sparrowhawk. Incompatible stories. Conan is mighty within Conan's story because he can butcher five guards who catch him stealing the jeweled eyes from the idol of The One Who Coils. Sparrowhawk can change his shape at will and kill nine dragons solo, which is the standard of might in his story.
Each tier (apart from the fail tiers resulting from poor class design) corresponds to a type and scope of story.
Maybe what we really need is tiered versions of each class stereotype... tier 1 fighters who emulate Cuchulain and the Stone Monkey, and tier 3 wizards who can't fly, teleport, or shapeshift.
