"I remember the battles that Oscar Pistorius had to prove that his blades did not give him an unfair advantage against other runners. It took him 5 years and numerous court cases to do this. Why hasn’t this happened for TIMs?"
Let's take the case of the transabled -- people who don't actually need a wheelchair, but feel as if they should (I kid you not!). Suppose such a person decided they wanted to compete with wheelchair athletes in the 100m, say. Just because they are using a chair during the race, won't alter the fact, say, that before the race the fact they can stand means they can undergoa different training regime. So, what they can do before and during their personal sporting development matters, not just what their capabilities are on the day (where they are in a wheelchair just like the other athletes). And perhaps because a key factor in parasport is the correct assessment of actual capabilities and hence meaningful classes and competition..........
So, just as the transabled couldn't enter because although they gave the appearance of being disabled, and seemed to copy the capability of a disabled athlete on the day, they weren't actually disabled, so perhaps we can see although a transwoman athlete may give the appearance of being female, and seem to copy the capabilities of females on the day (by having lowered testosterone levels), since they're not actually female..............
Seems mad having to go that far to make an argument as to why it is unfair, but I think we have to look at it from the wider sporting angle, and expect the same criteria to apply as have already worked reasonably well in parasport.