Oh man, i am getting nostalgic for 4E. Epic Destinies were surprisingly simple constructs and yet really worked well to sell their narrative and make you feel Epic.
As with far too many things, I suspect the power level being asserted is the power level of skillful, intelligent players....who have gotten a Wizard to 20th level with a goodly supply of powerful magic items. Because Wizard spells, at least in AD&D, kind of had "whatever you can get your GM to agree to" as their power limit, and were thus functionally unlimited unless the GM was particularly draconian about it. (Which must have been exhausting! I have no idea why anyone would want a system where it only works if you choose to be a pernicious dick about every tiny error...and thus get hoist by your own petard should the player make no errors!)