Chennai Super Kings are obviously one of the best teams in the IPL so far. I will also say that there have been times when CSK did not have the best team in the tournament on paper. But they had a really good captain. They also had a team which always listened to MS Dhoni. That's why I believe even without the best resources they have been able to be successful. RCB does have a good team. At least in most cases. But they lose crucial matches.
Are you sure about this? You are claiming that CSK has better players when compared to RCB. Think again. Because RCB has some of the best T20 players in the world. In the batting department they have Faf du Plessis, Virat Kohli and Glenn Maxwell as the top-3. Then they have promising players like Finn Allen. As the keeper, they have the best option available in India - Dinesh Karthik. And bowling is also top notch. They have Wayne Parnell, Harshal Patel, Josh Hazlewood and Mohammed Siraj as the pacers, and Wanindu Hasaranga as the spinner. You still want to say that CSK has better players? 
If we make a comparison between RCB and CSK it is easy to find that RCB team has few players who are very much strong. They have good reputation in world cricket as well as franchise cricket. But compared to their players I don't think CSK had such reputable batsmen or bowlers but their skillful leadership and quality batting and bowling made them champions. Even with a good team in IPL, RCB can not win the championship from any session. A good observation of these two teams RCB and CSK will make it easy to understand the importance of captaincy especially Dhani's contribution.