If your child is keen and a strong ball player, you probably want her to join the team that will contend for the championship. On the other hand, if your child is a marginal sportsmen, you may want him on the team that will contend for third place.
At least that's the conclusion I came to from my first season coaching (assistant/manager) a 10-12 yo ball team. In our league the teams start out reasonably equal (there are some inequalities with pitching that can't quite be eliminated), but at the end of the season there's a wide range of abilities. There are really three major determinants of success -- coaching input, chance (injuries), and natural selection.
The natural selection bit isn't hard to game. If you drive hard, push a bit, yell a bit, tone down the encouragement, it's not hard to eliminate two or three of the weaker players. If your numbers get too low you get to bring up the very best players from the lower league -- who will play well above the weakest players you gave up. I really doubt this is done consciously; I think these coaches would be profoundly offended if the topic were broached. It's just the way the world works.
The winning team this year had a superb coach (I've been learning from him) and, as near as I can tell, just this kind of natural selection. I suspect it's a universal rule in all team sports, no matter how egalitarian the league. On the other hand, I think in a league of nine teams a very good coach (better than I am now) can probably contend for third or fourth place with their original squad.
BTW, the optimization problems of a full-rotation 14 player ball team roster are pretty darned impressive ...