Reason why MS Obito is the strongest shinobi alive.
When I say alive , there are no Edo's and dead people .
Kamui is the reason . Kamui > your favorite . Let alone Rinnegan Obito , who can stomp all alive people . ( Though Kakashi would be a good match ) .
Now , if Kakashi has no intel on Kamui ( which he found out during the war ) , then Obito takes this low difficulty . But , if Kakashi has intel on Kamui , then , it would be either a draw or Obito's win . Obito can spam Kamui cause Senju DNA , while , Kakashi has been spamming Kamui lately 'cause Kyuubi's chakra . Obito > full intel Kakashi high difficulty .
BM/BSM Naruto is not a problem . Naruto would never find out how Kamui works , and if he knows , he can do shit to it . Bijuu Dama is useless to Kamui . While , Obito kept up with BM Naruto's speed . MS Obito > BM/BSM Naruto .
Sasuke is not a problem .