2) it does not work like "power leasing", so attacker actually needs to generate block using every key == waste of time and resources, while meanwhile main chain is going forward...
2) "Waste of time and resources"? I doubt it's that hard to harvest with 1000 accounts at once, PoI has PoS in its core, not PoW.
But if I understand correctly, "power leasing" merges leased power, so it's even easier, as you only need to generate one block in NXT, right?