But the goal of balance is for every player to have, over time, to have roughly the same amount of time in the spotlight and equal fun.
Building off the already stated "Batman and Superman" vs "Janitor Joe and Superman," one of my big issues is generally that it is actually really HARD to actually pull this off. That is, Batman on paper reads like a ridiculous Mary Sue: "I'm a world-class, beyond-Olympic athlete, one of the smartest men in the world, attractive, rich beyond the dreams of Avarice such that my entire superhero lifestyle can be hidden in a line item in the financial reports of my global business conglomerate. My parents were killed when I was eight which is what gave me the motivation to save others from suffering that kind of loss. Oh, and the man who raised me is a badass former British secret service agent, my adopted son is a similarly orphaned incredibly gifted gymnast and overall very sharp kid, and my main love interest is one of the world's leading catburglars
and also a rich socialite with her own multimillion corporation." By comparison even Superman, the Man of Steel himself, begins to sound surprisingly restrained.
Playing favorites in this way in order to compensate for the phenomenal cosmic power of magic has a very real risk of fostering jealousy...and of course the irony is that both sides can develop bitter feelings toward the other. Like siblings who each resent the other because the younger one got all the attention and forgiven for all their errors, but the elder got all the authority and respect.
Changing to this style from trying to balance everything around my own party
I mean, I'm probably in the top five advocates for balance on this board, and I will always tell people to STOP doing this because it's not good gameplay....so....good?
The two most pernicious falsehoods about game balance are that it has to be perfect and is thus impossible (when, in truth, balance within a defined acceptable range is both totally achievable and very effective), and that it must be keyed lockstep to player progression (which is patently ridiculous and leads to a greatly impoverished experience).
I don't want any one player, group of players, spells, or abilities to take over the whole game, but I also don't want all players, spells, etc. always to be equally powerful. The beauty of clever combos is in the way they short-circuit the ordinary game balance, and I never want to discourage from my players' cleverness in devising such tricks. I think of it analogously to M:tG: if there are no heavy power cards and combos, the game loses its appeal.
So I do want to be careful about maintaining a certain measure of balance, but never so much that sneaky/clever players can't break the game and take us all to unexpected places. I like unexpected places.
I value all of those things too. I see literally nothing that prevents such behavior in a well-balanced game. Indeed, your use of M:TG is a lovely example, because it IS a game that strives very hard for balance
so that those clever plays have greater impact. When a game is unbalanced, it features dominant strategies, which will crowd out other approaches unless someone finds a way to make a non-dominant strategy so massively useful that it can't be ignored. In a well-balanced game, by contrast, subtle interplay becomes the key difference between victory and defeat; the small contextual differences matter, and a careful plan that actually factors in the situation at hand will almost always be superior to just following the tried and true playbook.
Or, to put a spin on Anna's lessons in the Art to Atrus, "Balanced systems stimulate creativity and strategy."