I deliberately did not include any normative information on my post. Also, I didn't say the distinction was totally arbitrary (because it's not — social constructs rarely are totally arbitrary). I said the boundaries are fuzzy.

I think a regime where intersex cis women, as well as trans women who have been on testosterone suppression for a long period, would probably be most fair. I don't think categorical bans are fair in any respect, not is forcing intersex cis and trans women to compete with men (because they're likely to be much worse due to not having as much testosterone), nor is creating a third category (because it would have too few people to be truly competitive). But I'm not an expert and most likely neither are you, so I try to keep my opinions here relatively loosely held.