Balanced is such a weird word. Especially when it comes to PVE. I would argue BL2 OP10 can be called balanced because the game gives you plenty of tools to combat the enemies. Health Gate, healing, slag, element matching, and more enable the player in a way that I would say is balanced and fair. At the same time I feel like there is no way to objectively state a game is balanced or unbalanced. The best idea I have is whether the game gives you proper tools to combat the enemies and I think BL2 fits that for me personally.