Mumbai was a bit lucky, it is true. Also, we did not see a better performance from Mumbai's bowlers. If Jasprit Bumrah could not have bowled in a controlled manner, Mumbai would not have won this match. Bumrah gave away only 27 runs in 4 overs. Besides, we saw better bowling from Ashwin Kumar in the death overs.
"Fortune favours the brave", MI didn't let the match to go away even after the terrific start from GT and Hardik took some chances and it worked. But not bowling Santner was a big mistake in my opinion even though two left handers were at the middle because he got good record against lefty too and could have controlled the run flow in the middle overs. But it worked so nobody is gonna blame the choice.
Hardik Pandya used 7 bowlers in the match. He changed the bowlers to counter the batsmen. Since they won the match, it must be said that he was successful in his strategy. If a few players had been reduced, there would have been no such problem in the match. Mitchell Santner was bowled only 1 over. If he had been given a few more overs, I think he would have been able to take a few more wickets. Mumbai team looks quite brave because they have some young players there and they performed the same way on the field in the last match.