Your question is a bit strange. Revisionism is indeed bad. Let’s take Kautsky. Kautsky was not worse than capitalism later, he was a part of it. But where did you get it from that “ultra-leftists” think like that? There are just so many ultra-left groups and currents historically.

For example, there are anarchists who think they can “escape” from capitalism by owning a piece of land, practicing self-sufficiency and founding a commune. Of course, this is all nonsense. But it’s not as if they stand up and are allies of capitalism and imperialism.

There are also anarchists who think Russia is so bad that it is the lesser evil for them to cooperate with NATO.

Anarchists are ultra-leftists. But there are an incredible number of differences. There are also ultra-leftists who are not anarchists of course.

Speaking of anarchist. They were helpful in the Ukraine during the civil war and allied together with the red guard. Afterwards they were suppressed, but helped again and again against the Ukrainian nationalist and the whites. They were ultraleft but not allies of capitalism.

Ultraleft is something very broad. You can maybe say, that “in the end” they are helping capitalism and this applies. But that they all are that way how you describe it, I deny it. Some of course. But I can’t remember for example that Bakunin as example were this way.

I am talking about anarchism because “ultaleft” absolutely applies to them completely.

Edit: Made something bold