Many of the players currently playing in the premier league would like to have won what some of the "has beens" playing with Bunratty B have in their time. Newmarket B have a good young team while Kilkishen and Corofin B would be able to hold their own with most as shown by Kilkishen recently in the cup.
Nothing wrong with players deciding that they can't commit to the degree required for Premier Soccer or equally with not having the fitness - each to their own. In my experience most teams in the top half of their division would be able to give a good account of themselves against premier opposition. The top premier teams on form could beat them well but it is the better fitness and pace the game is played at of these teams that really make the difference.