I was a serious amateur marathoner for years, and even as a cis man, I can identify with your last statement. Running is a very special sport. I think most runners (with perhaps the elite tier aside) are competing against themselves.
We all work on our PRs. We all challenge ourselves to be our personal best. And while we can love to compete, we all run knowing that people out there on the course are faster than we are. Some are much faster, gender notwithstanding.
I’ve never done an ultra, and with my age relentlessly increasing, I probably never will, but the events fascinate me, particularly by how they upend gender expectations.
I’m happy to see sensible new rules being put in place for running events, but I join you in wondering if gender should be used for placement in ultra events at all.