They gave a couple examples of the kind of AIs that don’t make games fun. One was some game (real or hypothetical) where you fight a small drone that’s very smart and fast, so it’s hard to shoot at. Another was where the enemy goes off and concocts a sophisticated plan to beat you.
They described how the player wants to feel like the game play is about themselves, not about some ultra smart enemy. So big and dumb enemies tend to work best, even though they don’t use sophisticated AI by today’s standards.
It was like the the Jurassic Park meme: just because we can doesn’t mean we should.
(Also very strong agree on monster infighting, it added so much depth, as a kid I didn’t even know monsters could infight until the level with cyberdemon and arachnotron in the same room)