Why does Rumpel want to beat Regina? Why would he care about that?
She is just a secondary problem and always has been. The curse was to find Bae but Regina enacting it meant she had power and in SB without power he cannot do what he needs to do. In FTL he became to dark One to keep Bae but power got to his head. Regina just got in the way and after the Belle incident it seems to suggest they had been going at it for a while. It seems like they are playing a game in FTL while in SB he has a purpose and Regina is impeding his efforts.