Well okay, "from what I heard", then. Admittedly, what I heard is that he had a liking for burning Catholics, eating babies and drowning kittens, so the accounts in question may have been slightly dubious.
Revisionist history tends to work that way.
Ireton was pretty successful too. If he'd survived to succeed Oliver rather than the weakling Richard Cromwell, the army would have supported the Protectorate and we might still be a Republic today.