Generally, even in modern relationships, muscle is a better omen when "scouting for a partner".
Muscle means that this person is healthy, that they train, watch their diet, take care of themselves and have great discipline. And as the old greek already knew: a healthy mind in a healthy body.
Modern relationships are not anymore for just popping out kids. They are to make the two (or more) involved HAPPY. And that works better with someone of healthy mind and sanity, than someone who definetly got a few screws loose. I mean, I dated a borderliner for two years. That psychological abuse I wouldnt even wish my worst enemies tbh. Or try dating someone with severe chronic depression and see how they maybe not even intentionally suck up your energy and your will to live.
So no, if I want a partner, I want them strong in body and mind. Add that to the fact that my stone-age-wired brain still is triggered by the fertility-aspects, and you got even more reason to put someone like Sejuanni over a skinny topmodel.