It also largely affects the planning and flow of the team from year to year. Exactly as you mentioned, it affects the way candidates are selected for the next level. Doesn't mean they can't - just that across the board it is going to be tougher when you are competing against a lot of similarly talented players that are younger.

There are also quite a few athletes that don't come back at the same performance level they were before missions. I knew several athletes who were very similar in ability, and when the mission ones came back, they were far surpassed by the other's who hadn't gone on missions. Some of them picked back up well when they got back, but were basically 2 years older by time they reached that same ability and remained behind the others.