I do not consider that to be a good thing.
The concept is just bad, unless your goal is to prevent women from being able to make a living playing professional sports.
Please let go of the need for this.
I won't respond further unless you pick an example sport, and propose how your "scissor for ability" would work, in concrete detail. If you do this, I will be happy to explain why this would result in neither women _nor trans women_ having any chance to make a living as professional athletes.
Currently, with sex-based categories, a woman can be declared "the best in the world" and most people won't waste much time on the question "yeah, but could she beat the best men?" (granted, some will). They will accept that, e.g. she has the fastest time over 26.2 miles in the world right now, even though a few hundred or a few thousand men worldwide are faster.
If you use performance based metrics to create the categories (the way that road cycling does, for example, though still within gender divisions), that "title" would go away, and likely a woman would only be "the best in the world in division X", other than in (as you noted) some endurance, climbing and gymnastics sports where an elite subset of women could potentially be the best of "top" category.
It isn't completely obvious that this is a negative - how much of a change it would be would depend on a lot of other changes (or lack thereof) in how sport was organized. Certainly if it continued to focus on only the top division, then women would be shut out of most opportunities to be professional. But that's not inherent in the design. I do concede, however, that it is quite a likely outcome of such a category structure.
In elite sports, no one wants to see "best in division X". They want to see the best hockey players, the best golfer, the best skier, etc. The money incentives are considerable.
This would destroy women's professional sports.
I personally think that we'd live in a much better world where you compete against others who broadly speaking are in the same performance category as you.
But I do appreciate that the transition to such a world would, indeed, destroy women's professional sports, and thus I do not attempt to really advocate for that transition. If it could happen overnight (it cannot), perhaps I would, but that's not where we live.
The merr existence is not an evidence of success.
Kids' little leagues also exist, but can't be compared, with actual professional men's sports.
Where is women's American football? Women's baseball? Crickets...
Women's icehockey is in such a state, that there are only 2 decent countries dominating everybody, and they would get destroyed by men's amateur players.
There are only few women's sports disciplines that are actually popular on their own. Like figure skating and tennis. And the athletes would get annihilated by their male counterparts.
Since I personally don't have any interest in team sports of any type, I have nothing to say about your observations, though I will continue to wear my "I'm here for the women's race" t-shirt whenever I can.
Yet you would hapilly abolish them and think the world a better place? Im genuinely confused.
Would you wear a "division 2" or "slow bracket" shirt with similar gusto?
Categories would be assigned based on performance criteria for the sport in question. One simplistic approach, loosely modelled on how road cycling works, would be to have categories based on race performances - you enter an "open" category, and after N finishes above a certain level, you are required to move up to "division 4". After N finishes above a certain level in div4, you are required to move up to "division 3". And so on. The idea is that you're racing against your performance peers, regardless of their gender (or age).
I'd happily wear a "I'm here for the D2a race" shirt in such a system.
Most people's paths as sports participants (not spectators) is that they enter a tiered system and remain there. Only a tiny percentage of people rise through that system to become truly national or internationally competitive.
One of the central problems here is that there are conflicts between what's good for the participants and whats good for fans/spectators. They are not always in conflict, but in several important ways, they truly are. 99.99999% of people who run marathons are not Eliud Kipchoge, and are not interested in a system that is designed around his level of performance and competition. But 90%+ of the people who would pay to watch marathons have little interest in a system that isn't built around talents like his. The same is true of almost all sports - solo or team - but it doesn't show up for 80% of them because there is no market for paid viewing of them. Or rather ... there wasn't until YT became what it is today. "The Finisher", a film about Jasmin Paris, the first woman to finish the infamous Barkley Marathons, has had 1.8M views, something it would never have achieved in "legacy" media.
Did you actually think that lean mass would be a sensible way to separate divisions in a gender neutral fashion? That would, again, just result in women being unable to compete professionally in virtually any sport. They would be relegated to Division N, for some very large value of N. Competing alongside multitudes of biologically male amateurs, where nobody cares and nobody pays to watch. To even entertain this idea betrays a total lack of understanding of the matter at hand.
Right now you are acting like Elon Musk storming into the government and having 20 year olds cut everybody's budget. You may think you're coming in with fresh outsider perspective and an open minded way to look at things and improve them, but everyone actually involved in the domain can see a trainwreck in progress. It's not a good look.
I am quite certain it's not your intention, but you're really coming across as someone who hates women's sports, and doesn't want them to exist. On behalf of my wife and sister and a lot of the women I've known in a lifetime of playing sports - kindly keep your awful ideas to yourself. Women fought tooth and nail for the right to have their own professional sporting opportunities. Don't you dare try to take it away from them.
Fortunately, most people don't like to live in this hell and are against clear attempts to destroy women's sports by the clueless and/or purposefully malicious activists.
Really, the question seems better turned around: why use a known bad proxy for physical ability when another one might be better?
Pick a sports-relevant metric and split into divisions. Some sports will naturally fall into gendered divisions, while others will have varying degrees of co-ed competition among competitors of similar ability.
The way out of this is not to pick a better scissor of sex or gender, it's to pick a better scissor of ability.