he can't master it rofl, it just appears that when he has ms active he becomes intangible, it has no other ability how hard can it be. You see the first scene where shurinken are tossed at him he doesnt get hit, and he seems like he don't get it, when he then wants to attack he simply materialses, probably the easiest technique to master, though you need to be smart to get the timing right, but we've already seen Minato and Kakashi are way superior to him because of that.
I don't like the chapter either, a lot of time on a completely useless fighting scene which we couldn't care less about, but Kishi showed it and so far no plot holes.. The reason he is strong is just because of the zetsu suit, so what is OP is the zetsu suit, we can only wonder why the current zetsus are such fodder, but meh who cares, this one is probably special and made for obito.. You see zetsu said madara chose obito, so madara probably planned for all this, Rin, Obito, the mist nin, his only miscalculation probably was kakashi