Not exactly in the same situation, but allow me to offer some friendly advice....
Unfortunately, it sounds like you have too many people....if you could play 5 every nite, then a 2 person bench should be enough....with 7, basically everyone gets to play 2 out of 3 matches, and make it understood early...also, as you get closer to play-off's, weaker players should be willing to sit for the team more often, and you need to set that expectation up front as well....
We have 8 on our APA that I captain, which is basically 1 too many as it turns out.....ultimately, too many people have to sit, and some lose interest....
As far as the other players complaining, anybody can be an armchair quarterback....they weren't complaining when you were 8-3, and carrying that record while being able to keep 9 people playing and happy - that's a pretty good job IMHO....