So by being "fair" to the very small numbers of women with high levels, we are being unfair to the many more women with "normal" levels.
We (or that is the sporting bodies) would not be unfair to these women if the rule stated clearly that this special rule, created for women with a DSD, applies only to biological women and those who are indeed assigned female at birth because they looked more female than male on the outside - whatever's going on on the inside.
So levels below 10nmol/l for women and women with a DSD. That's it.
Then finally create proper rules for transgender athletes and don't just allow one group to appropriate a rule made for a completely different and unrelated group.
As for Caster and those like her - I've wrangled with this a lot, esp since I have friends whose kids compete at national level.
So forget about testosterone for a second and consider Usain Bolt for a second. Specifically his physiology. By some freak of nature the man has the exact perfect dimensions and proportion of leg bones to joints to overall size to bone structure and muscle type (ie skinny dude vs built like a tank), perfect lungs, perfect heart, perfect stride length for the short distances etc. I saw an analysis on this once and this is extremely rare.
That's why by some measure, for a lot of the time, no one stood a chance against him. What Mother Nature provided him with was superior to all of his competitors. Let's assume he didn't apply some hitherto undiscovered kind of doping but this natural jackpot of advantages was all he had. Plus his motivation, dedication etc.
Everyone less lucky than him just had to suck it up.
I could have brought up Andy Murray who is in the opposite situation. An exceptional talent, at any other time he'd have completely dominated at the number one spot for years. But the sport was blessed with three other, once in a century, exceptional talents. Which the laws of probability allow for, weirdly enough. So he had to share the top spot.
So, back to Caster.
In the interest of fairness and because Caster like all other athletes also has to sustain her motivation, dedication and training regime, remain illness and injury free etc AND is actually a woman (that's how her individual intersex condition works out), she should be allowed to compete but subject to regular hormone level tests (to make sure no one dreams of abusing the intersex rule and dopes with a little extra T).
That's just my personal view of course and it took me over five years to get here, but in the end it was actually the transwomen who did it. If I look at how fair this all is, then I would say favour these women over those men.