If a person is born/has spent most their youth in Ireland, they are Irish, if they have not, they are not.

I don't think it's that black & white really

I've cousins who grew up in England but literally all of their cousins live in Ireland, they did Irish funerals, christenings, weddings etc.. their entire lives. Irish surname, Irish traditions, raised by Irish parents.

Likewise I've a friend who moved here from Poland at 3, he's definitely more Irish than Polish culturally but if you asked him he's Polish raised in Ireland, speaks Polish (although also speaks English with a Cork accent) celebrates Christmas on the 24th

I agree that heritage means nothing if you're multiple generations removed, but I wouldnt say people raised in another country by Irish parents aren't Irish