I do not think it can come down to strictly numbers. It comes down to the coach, the program and the players involved. Some programs and coaches can handle Large numbers. They communicate well and everyone knows there role. Now can a players role change? I believe yes. We had a young man in my sons class. He got little playing time during Freshman, Sophomore or Junior year. The coach had talked to the player after his junior year and explained what he could expect his senior year if he did not meet certain goals. The young man came back his senior year. He did not meet all those goals, but he met most of them and was much improved. During cuts, he explained that he would be a PO, and get an inning or two depending on how things were going and how the rest of the bull pen preformed. One of those innings came early in the year, and he came out to pitch and had changed his delivery and was pitching side arm. Did he have a lot of velocity no, He was around the strike zone but not always in it. But he was very tough to hit. While the rest of the bull pen struggled he was relied on more an more. He turned out to be one of our better pitchers out of the Bull pen that year, and racked up quite a few innings. Was this a great team, no. It was a very young team with few seniors. But the coach did not dismiss him because the talent was not there, he never gave up on the kid, and he preformed very well. I talk to his parents often, we are still friends. His parents still talk about how much that season meant to their son and to them.
Did other seniors get this opportunity? No, Some of them came improved but not enough, and one that actually had some talent, was still cut, because his attitude and the example he set for younger members of the team.
Each young man needs to be taken on a case to case basis. You cannot and should not treat each one exactly the same. You need to asses and judge what is best for the young man, the other young men on the team and take appropriate action. Just because you keep one senior does not mean you need to keep them all. One of these seniors had lots to offer off the field and in the dug out, and practice. The other did not.