He seems to be very skilled at it and after having trained with Madara he probably is. My only query is why doesn't he use it often? It could be a powerful factor in a 1 on 1 battle.
Good question, maybe it's because it takes more chakra, maybe he is more skilled in kamui, and maybe he prefers kamui because it's easier to use in a fight, making it easy to win. Another question is: Why doesn't obito use the rinnegan abilities?