It was a defeat but the reason it's a big deal is that it was the death of the indigenous Irish aristocracy. In today's egalitarian Ireland this might not be seen as a bad thing but in practical terms they were the leaders and potential leaders of any fight for independence and it took generations to replace them.
It's also a very emotive story which has been romanticised for centuries and presented as a great loss to Irish history and the common Irish people. However there is no reason to assume that the tenant farmer or labourer would have faired any better under their rule than under English rule, at least in the short term.