In my headcanon, the movie takes place in the timeline where only Trunks came from the future
and the androids were shut down with the remote control. Piccolo is Kamiccolo. About the power
scaling, i have these possible explanations...
-Cooler got one more zenkai when he returned as multiple bodies.
-Piccolo was beaten by multiple Coolers, not just one.
-SSJs trained between Android Arc/Movie 6 and surpassed Weighted Kamiccolo, or at least closed
the gap so that they could succeed as a team where Kamiccolo failed individually.