Worse than the gap between those two authors: Many other such stories emerged when the #PublishingPaidMe scandal broke a few years ago.

I didn't quote more of them because they were extensively covered at the time, and--we can hope--some offending publishers have mended their ways.

Your advances sound reasonable to me (and because so many advances are unreasonable, "reasonable" translates to: good!). And I know the commenters are grateful for the reality check of comments like your numbers. Thank you!