Forget Foreign Players (We have at least 2 quality players & 2 above-average), the problem is with the core players.
We have only Virat Kohli who is a regular in National team. Apart from him Vinay Kumar is only a probable at current form (OK with him though). Zaheer has past his prime. Others are either below average or have not yet proved on bigger platform.
Whereas see in CSK there are 4 players - Dhoni, Raina, Jadeja, Ashwin all regulars in National Team. No wonder why CSK can win all matches and go on to win this year also.
I think RCB should have got at least 1 or 2 players who are regulars / closer to national team