Don't agree with any of your arguments. Let me outline my reasons why:
1. 18-39 year olds currently are only able to play once as it is. This isn't limiting your ability to play nor your opportunities to play due to the age restructuring. It is adding opportunities for the 40-49 year olds. I, for one, am looking forward to it.
2. You are not limited to playing only on a club team. That is your option, not obligation, to join a club and restrict your playing to only those teams. You can still play with a public park-based team.
3. I wholeheartedly disagree that 18-39 year old women are the "busiest group of women" that play league tennis. What a luxury to be able to "get away during the day on Fridays". Trust me, not all working women have that option. And look at it this way, if this age group is the busiest group of women playing USTA, it's a good thing you have limited playing ability as you wouldn't have time for more playing opportunities (see #1).
4. As for working mother having a hard time playing in the evenings or on the weekends, not true. I would think that working women have a more difficult time playing during the day as they usually work during those hours. Almost 100% of the women that I play with on all of my USTA teams are working women, most with children. There is no way that we are able to get away on a Monday or Friday morning to play. Evenings and weekends are when the majority of our playing time occurs.
5. I'm sure that your league match times are not occurring on Monday mornings when your children are getting ready for school. If I had a guess, I'd say the matches will be played when they are in school so I don't see what the problem is with getting your children to school and then going to play a tennis match, regardless of what day it is.
6. How nice that your local league coordinator has different options for you to choose from...day, evening and weekend. Not an option in most places.