>>36598797Depends on the team, but probably gen 4 from an average standpoint.
For what it's worth, I've played every gen monotype bug and 3 was the hardest. Gen 3 was when the NPCs teams weren't laughably bad, but at the same time plenty of pokemon still had fuckawful level up movepools. Gen 4 may be harder, but at least that was the gen when almost every pokemon got a usable movepool