“Whether Cromwell actually committed genocide is hotly debated by historians to this day.”
There are “historians” who debate the existence of the holocaust, too.
A more direct comparison would be to Chmielnicki Y”S who was murdering Jews at almost exactly the same time as Cromwell was murdering Irish, with almost exactly the same rationale. And yes, you can find historians who don’t pay attention to Chmielnicki’s genocide (particularly in Ukraine). The fact that Cromwell was in fact very good to Jews should not blind us the fact that in almost every other respect the man was a total rasha.