Honestly, It's possible he's stronger alive. Edo tensei seals a soul in a dead body. From tobirama we learnt that oro revived them weak as shit in part one. and, even in part 2, they weren't 100%. Sure, kabuto said madara was past his prime, but all he meant by that was madara now had a young body with his rinnegan eyes. For all we know, he coul dnever push his limits as an edo because of the whole having your soul tied to a dead body thing...
Exaar said:
Maybe he is simply saying that for when he Adds the Bijuu/Juubi to his own strength.
If anything an Edo form makes you stronger than your living form, Not weaker.
Not necessarily true. ET gives you immortality through a healing factor that replenishes you to a rested state constantly. But, that doesn't mean you can push your body to, or probably even past it's limits... You're still in a dead body after all, so it might not work the same. Anyway, madara probably has SM now.