As someone whose family was involved in the first wave of people who could be called 'English' invading and suppressing the Irish (and indeed were responsible somewhat later for introducing gunpowder to that country according to family legend!)...... - It was actually in the reign of William the Conquerer, and we got the Barony of Slane for our trouble. (Before anyone asks we lost it after backing the wrong horse at the Battle of the Boyne.)
I can assure you that we did not treat the indigenous Irish at all well - they were little better than slaves. But then so were all serfs..... The Irish were treated no worse than the Anglo-Saxons by the Normans. In later centuries the 'English' started to be better treated than any of the Celtic tribes, not least because those tribes tried to make life difficult for the powers that be (or were) - no doubt because they felt they were not being treated very well...
The biggest problem is that, like the Bourbons, the Irish forgot nothing (and learned nothing). They still harbor grudges from 1000 years ago.