Because ultraleft believe that revisionism is worse than capitalism, do they ally with capitalist to destroy revisionist?

Perhaps not Maoists. They usually follow the two line struggle, where they debate with revisionists to eventually prove that they aren't following a proletarian line, but a bourgeois one. For them, MLs are mostly misguided by revisionist party leaderships.

Things are a bit different in wars, where Maoists will fight revisionists in the wars they consider unjust (like in Afghanistan, where the Maoist party opposed the Soviet intervention with arms). The same applies to wars of aggression led by imperialists, like in Afghanistan 2001 and Palestine.

In those cases, they will ally temporarily with national libertation movements, even if their ideology is reactionary. That's why they defend the palestinian and afghani resistances so much, even if some sectors of those groups express reactionary ideology.