Whom is going to do a better job? A group of educated, passionate people that can troubleshoot their own problems in realtime? Or "Peggy" at Cloud Vendor X that deals with 400 other clients?
That depends on whether the fix that Peggy deploys for one client also fixes the same problem for the other 399.
In other words: It depends.
There's no general answer, because deciding where to draw the abstraction barrier between you and your vendors is an unsolved, difficult, and evolving problem.
