I'd like Outrage, to be honest. Maybe Kotetsu will use it as a last resort move?
Boosting + Outrage is a common scrub tactic. This might be a homage to that.

Only problem is that Ash doesn't really have a Unova Pokemon that can survive a rampage ...

At the absolute worse Ash will be out 3 Pokemon from a full-on rampage. Maybe Ash easily beats Ferrothorn + Two Others before this happens. Then Ash comes back on Hydreigon, Hydreigon's revenge'd by Samruott, and then we finally have a fair match albeit a 2 on 2 one.