It seems weird to attribute WoW's launch success to AI and not to the 20+ years of experience the industry has with modern online game architecture. When it launched in 2004 the state of MMO games was very different and a lot of those choices are hard to undo on an actively played game. I imagine AI was used but I doubt it had any great architectural insight that the experts at Blizzard didn't.

My belief that AI may have helped Blizzard plan, set up and smoothly launch WoW Forever is inferred and based on the poor quality of their other recent launches. WoW Classic released in 2019 and was a laggy mess for the first few days. Blizzard recently said WoW Forever is their biggest launch in history for peak concurrent players, bigger than Classic or any expansion they've released including Burning Crusade and WotLK.

Blizzard has long been derided for its poor performance when handling massive player events, showing worse performance in that regard than large private servers such as Nostalrius.

The biggest technological advancement in the past couple years that could help explain their sudden and dramatic improvement is AI, in my opinion. I think it's fantastic if AI is indeed a large part of the reason for their rapid improvement.