Up until now, Madara didn't use his Juubi Power to his fullest extent. Throwing the dark spheres can't be the only thing he can do, can it? Thinking back, Guy is litteraly breaking Madara into pieces, throwing him around with his Eight Gate. But still, Madara laughs at the fact that he is being controled by him, and also because he's alive now was well. Then what's with Madara's "happiness" in all this? He has the power of a god now, and Guy's just giving him the beating of a lifetime. Even Obito did something better with that same power than him until now... Could it be that Madara's holding back, or is Guy just THAT powerfull that can even defeat the power of the Sage of the Six Paths?
The sole fact that Madara is laughing and not destroyed the slightest bit is evidence enough of how strong he is. Of course he's holding back. He doesn't want to kill all those people, so why should he?