I don’t think it’s about power creep. It’s about separating player power from items that enhance specific skills in very specific ways and the very, very strong interactions groups of legendaries can have.
Diablo 2 dodged this pit (either accidentally or by design) by having the generic “+skills” modifier. Buffing the skill itself can make it useful. In Diablo 3, the skill needs supporting items. They added maybe a dozen builds to D2 by buffing skills in the latest patch. In D3, it would have required adding/modifying legendary bonuses or sets.
Diablo 3 can feel real crappy at max level because that one skill you want to use really can’t be used because there are no good builds behind it. While leveling, you can generally use almost any skill you want… until you find a legendary that gives a massive bonus to a particular skill and then you have to use it if you want to level faster. I don’t think this is necessarily bad but there just aren’t enough items to cover every rune for every skill and only a few dozen builds out of the potential thousands wind up being any good. I still have an axe to grind about changing Etched Sigil to be specifically about tornadoes ruining my favorite build in the game (Arcane Torrent/Meteor).
And of course, while some players say “we don’t want power creep!” there will also be people complaining, “stop nerfing the fun builds!” You can’t have both.