The obito in the present is not alive he a part of mazou.
Madara says when you feel pain you know you are alive
He does not feel pain (against rasengans from minato and naruto)
When he was alive He was synced to gedo mazou, a part of demonic path and juubi.
When activating MS he partcially synced to juubi, thats where all the woooooooh comes from.
So in conclusion, the obito naruto is fighting is not the same obito before unlocking MS for he linked a bit to mazou or likewise it is the same obito just linked to the mazou later
Oops i forgot to also say naruto joked about tobi being in pain when mazou was knocked down and tobi was like what do you mean, of course naruto being im imagining it
Also tobi has stated that he can not part with the gedo mazou