Handling both captaincy and maintain good batting equally kinda tricky things and not everyone suite for that. It's a long time individuals are beginning making question on his captaincy and there make sense to hand over T20I captaincy Rohit Sharma since under his captaincy MI won the IPL trophy.
The only reason everyone is claiming to hand over the captaincy to Rohit Sharma is because of the performance as a captain in the IPL. The difference is that whenever Rohit Sharma did not play due to injury Pollard was leading the team and they were winning them as well and it is all because they had a good complete team with top bowlers and good openers and middle order as well and leading a strong team is always easy 
.I have to agree with you here. Pollard performed much better than Rohit, as far as captaining the Mumbai Indians was concerned. But then the question is who can replace Kohli as the captain of the Indian team. All the top captains during the IPL were foreign players, such as Pollard, Smith and Warner. So the choice comes down to Rohit Sharma and Shreyas Iyer. And at this point, I have to say that Iyer doesn't have enough maturity.