What Cromwell did to Ireland was heinous.
Cromwell was only in Ireland for a year quelling a rebellion. What the English Kings did during the Irish potato famine was worse.
Also, as far as crimes against humanity, Catholics sacked Magdeburg Germany in 1631 during the 30 years war and killed 20,000 out of 25,000 after the gates were breached during a siege. So it’s a high water mark for the period. Drogheda was a lot less than that around 4,000 according to Wikipedia.