There's probably some Irish hurler who we've (by which I mean me) never heard of who's a better athlete than Conor McGregor.

Do you mean DJ Carey? 5 All-Ireland Hurling titles with Kilkenny. 10 Leinster titles. His Wikipedia page doesn’t even list his win record in Handball (GAA squash without a racket), but he has multiple All-Ireland titles there too.