If you watch DC's 3 matches against MI,  you will see that DC has lost 3 matches in a very bad way. MI is the only team in this IPL who are very stable and each player has done their respective responsibilities properly. The rhythm of all the other teams has fallen. Some matches played well, some matches played very badly. When playing against a strong team like MI, DC's players should have focused more on their own performance.
 The difference was the quality in the MI bowling line up, i just came to know that Trent Boult was let go by DC and trade him with MI and that came back as a harsh decision as he troubled them the most along with Jasprit Bumrah and when you have two world class bowlers in top form bowling at tandem no team would score freely without taking the risk and that would lead to wickets.
If you take the final match, DC was able to stablize and build a fourth wicket partnership because Jasprit Bumrah and Trent Boult finished their spell and i still believe that if the captain would have continued with them the situation would have worsened.