Except...That doesn't realistically work
When a champion is weaker than the rest of the roster, even the balanced champions, it's significantly more work to nerf every champion stronger than them than it is to buff that one champion.
Yeah, nerfing strong champions will buff weak ones, but not significantly, especially if the champions at the top aren't a counter to that champion.
"Power creep" only applies when past things are static or largely static, like in Magic, or even Pokemon (specifically the video games, but also applicable to the trading card game), either because of design decisions (e.g. no pokemon base stats changing between generations, barring situations like the special split), or because it's literally impossible (when the game is in print on numerous small things like cards, it's pretty hard to actually run a patch since you'd have to change every instance of that card, and if it's a nerf people simply wouldn't do it).
Since everything in League can be patched and changed to balance it with the rest (and Riot's actually willing to change those other things, unlike other companies that don't despite the fact the ability exists), power creep is more or less an impossibility.
