We had this exact kind of situation and discovered the following: for our family, the important thing is not the size of the commitment, but the flexibility of the commitment.
So in soccer (at her particular club), there was little room for flexibility. If she missed a game or had an injury, it was a big deal to her teammates (she was keeper). If she missed practice, the coach wouldn't put her in to play. If she didn't participate year round, she was looked down on. It was a huge burden to our entire family because of the lack of flexibility. My daughter suffered several overuse injuries. She missed out on stuff she really wanted to do.
In swimming (in her particular club) there is lots of room for flexibility. She can go up to four times a week, but she doesn't have to go four times. She can decide to skip a practice because of a) the need to heal muscles in order to avoid injury b) massive homework c) other obligations d) other fun stuff. She moved from the third tier to the second tier team and the practices got a bit longer, but still flexible in terms of frequency. If there's a meet, she can sign up or not, do one race or several, etc. If she doesn't complete, it doesn't affect the other kids' ability to complete or to do well.
My daughter is super-athletic and loves to swim, so she's been going four times a week. But lately, she's been feeling really sore in her shoulders and a bit overwhelmed with schoolwork, so we are scaling back.
