you'll have a new mechanic to level up that will be important for your ability to "challenge threats" specific to the DLC. So the core loop - challenge too hard I'll go explore elsewhere to get stronger - is maintained, regardless of how OP you are in the main game. This could be a new defense mechanic for enemies you need to break through by collecting xyz, killing mini-bosses etc, I think attack power in Sekiro is just an analogy so it won't be a straight-up damage boost but something else entirely.