In my opinion, Rebel Óg should run league and championship at each age from U12 to U18. Not sure when things changed from that arrangement or what the reason was. Rebel Óg's predecessor, Bórd na nÓg, ran league and championship competitions at each age. Everybody understood it and it was easier for clubs to fill a team by having players play a year up as well as their own age.
Now, clubs with small numbers who, for example, may have fielded an U13 team consisting of U12s and U13s will have to field at U15 the following year if there are no U14 competitions. This means that some players will be playing 2 years ahead with the remainder playing 1 year up. It's not possible for such teams to be competitive and it becomes very disheartening for the young players.