Hmmm… I think you got the light themes reversed. If anything, Breakers has (a tiny bit) more contrast than Sixteen. I agree that you can’t please everyone, but I think if you only have 2 color themes per background (which I think is enough for the default set), one should have be really high contrast. Slush&Poppies has good enough contrast overall. The colors are darker and more saturated that either of the 2 new light themes.
Pls remember that not everyone in your target audience is twenty-something years old with a 20/20 eyesight.