They were not wrong.

I'm EXTREMELY jealous of my partner's older cousins who are now grandparents and specifically stipulate that their kids drop their grandkids off at their house every other weekend (!!!!) so that they can devote it to themselves.

If that's not a good-marriage hack, then I don't know what is! And their parents KNEW it! Because when that's NOT happening, the weekends are almost 100% kid-focused. It is absolutely overwhelming, even with breaks here and there.