I don't think reservations should be stopped - the point of them is to be able to make sure you get a seat on a busy service. What's the point of reserving a seat on a quiet train?
But Irish Rail should have somebody managing boarding if they have reservations. Because reservations are relatively new to the Sligo line, a lot of people arriving early to get a seat, sit in the wrong place and then end up either having a fight or standing because somebody with a reservation turned up 5 minutes before departure.
Irish Rail should have to surrender the reservation fee if you don't get your booked seat and the entire ticket price if you have to stand. The current situation is that they refund the reservation fee only if you have to stand.