The attendances at the Schools' Cup final is a symptom of the major problem in Ireland: people who go to the big event and not to games every week. Saying that more people go to a one-off game than to another one-off game is no reason to say that rugby deserves more coverage in general than football.
However the biggest problem is that the media coverage of Irish football is terrible, not that rugby gets too much coverage. If the papers had less coverage of the AIL or schools' rugby, what would they replace it with? More of the same; more GAA and more British football.