Am I missing something? The mod post first says that there is a study by Joanna Harper that "showed that as testosterone levels approach female norms, trans women experience a decrease in muscle mass, bone density and other physical characteristics". Reading the study though it is just a review of marathon times by 8 runners before and after transition and didn't measure physical characteristics.
Then the post mentions that there are additional studies to collaborate Joanna Harpers study but the Cosmos article doesn't actually mention any.
Then the third study isn't really a study but a literature review that cites the previous studies.
You are right in the sense that the science isn't actually settled on this issue. Apart from the frequently-cited 'bone density' and 'muscle mass' issues, there are also questions of quadricep-angles, bone structure differences and the like. However, even in the latter cases, it's completely unclear whether men have a substantial biomechanical advantage simply by virtue of the shape of their pelvis - or, at least, whether it offers an advantage which falls outside standard natural deviation between competitors in the current female divisions.
In any case, the most objectionable aspect of this is really just the laziness. It's relatively clear that the US IPF affiliate hasn't taken a scientific approach to the issue at all and is simply trying to circumvent the issue by citing the standard objections. It's also a bit of a laugh given the widespread usage of PEDs in the sport.