For me the answer is pretty simple. Scrap the O’byrne cup (and their equivalent in other provinces) and also scrap the inter county league competitions.
The county season will run from June to August every year and outside of these times, players are with their clubs or resting. Players can only be on one panel e.g. if a 20 year old is on the senior panel, they can not be on the U20/21 panel. Same goes for 17/18 year olds playing U20/21.
Run the club leagues off in Mar & Apr, club championship in May and Sept, and club league in June, July, August. Players are selected for county panels based on their club form. They then go to their inter county “camp” (similar to soccer and rugby) for the first two weeks in June, with the intercountry championship starting mid June and running in a champions league format over the Summer. Colleges can play their games in Jan/Feb as is.
It would solve a number of problems in one go including the fixture mess, it would address player burnout, it would give clubs more access to their players, it would reduce the training to match ratio and most importantly it would give club players a set fixtures list at the start of every year that could be adhered to.