if this is an issue that ever comes up

I am female with two male partners. Before my first partner had other relationships, he sometimes asked for more time with me, but actually seemed less concerned about partner balance than I was. I strongly prefer for us to be in relationships that take up approximately equal amounts of time, so that I don't feel like anyone is sitting around waiting for me to pay attention to them.

This is merely an anecdote and obviously doesn't mean your concerns are not valid. :) But, also a single data point, there does exist at least one female partner who does not see it as a competition, and whose sense of justice is offended if everyone isn't having at least as much fun as they would like. :)