Titan EX is a thing that really does bring out the worst in people. In your case, unfortunately, it's also a duty that is extremely tank reliant - if the tank loses aggro for even a couple moments or tank swaps at the wrong time it can cause a wayward Mountain Buster to wipe the entire rest of the party at once, or several other horrifying things to happen.

I would not suggest entering into Titan EX for "gearing up" your tank, or any of the EX Primals, really.