Honestly, if Blizzard hadn't started to incorporate mods into the default game they would have eventually caught themselves in a pickle. Because they spent a lot of time designing the game around the assumption you'd have a bunch of them, to the point where the game was impossible without.

Like, good luck doing most raids without some DBM knockoff (eventually most bosses gained an energy bar and buffs to denote a lot of that) and outside communication (they had a whole patch for an ingame voice chat that never got used). Or even leveling without ol' Carbonite or the other (all quests now show where everything you need is).

So its less QoL they are taking credit for, and more being so fucking lazy for so long that they built a game that required some external programs to be playable and then realized that had a lot of potential to bite them in the ass.