Well, I had some conversations this weekend with a few high level people on this very matter who have played 3, 5, 7, and 10 man on Am and Pro levels, and they generally said that they like having different formats around because it gives them the chance to play more ball. True, said they, that there are adjustments to be made and it can affect the way their squads balanced and thus the results that they get in the end, but it allows for different configurations, different field possibilities and the moves that each present, and more flexibility for the people putting on events. This is pretty much what we want. If you have 2, 4, 6, or 9 teammates to play with, then play what you can put together. It's like the Olympics, where you have people that tune themselves to run certain distances, jump high or far, throw something round, flat, or pointed, etc.
Keep them all around.