The parental worry about ECs stems from the older view of the importance of being well rounded. They are countless reasons to be well rounded, but its importance in applying to college as an athlete is not one of them. Colleges are not necessarily looking for well rounded applicants, they are looking for a well rounded class. If your son is a D1 caliber soccer player, chances are he is not the star of all of the high school’s dramatic productions (and vice versa). But colleges want both good soccer teams and good dramatic productions. So, they are looking for the standouts in the various areas. Most standouts concentrate in the area in which they stand out.
I am not advocating that athletes give up on non-athletic interests. To the contrary, they should participate in any activities that they enjoy doing. Parents, on the other hand, should not worry so much about whether their athlete has focused too much in one area and needs a broader base of ECs. If an athlete spends 20-30 hours a week on a sport, there isn’t going to be much time left for other endeavors, and that allows for only superficial EC involvement. Colleges want depth, and not breadth.
Nor am I saying that other EC involvement has no impact on an athlete’s application. I just think that the impact is so slight that it doesn’t justify any concern. Put differently, if Princeton wants you to play LAX, I don’t think they care much that you dropped out of French Club after freshman year.