Every level is improve or be replaced. Every year new "top" prospects are brought in. I saw a Power 5 player go from freshman starter to soph platoon player to junior backup to told he would have to make the team senior year. He passed. He got the message.
Over this player's tenure the program improved immensely. It raised the recruiting bar. The player peaked freshman year. He didn't improve after arriving at college. Better players came in every year.