Well maybe he can convince me when he passes by this thread again, but i can't see how obito can beat pain.
Blasting him with rockets + The dog summon raging him, crab summon blasting him with water, and pain flying out of range effectively enough counters Kamui. If obito ever manages to kamui, the visual field of rinnegan stops any attempt at flanking and as soon as he pops out to attempt a kamui, shinra tensei blasts him the second he tries to beccome tangible seeing as ST is as instant as kamui and takes no movement to do.
really, all obito can/ever does is kamui. Pain can counter that no diff and with enough fighting he'd analyse kamui enough.