From your link
Harper analyzed self-selected and self-reported race times for eight transgender women runners of various age categories who had, over an average 7 year period (range 1–29 years), competed in sub-elite middle and long distance races within both the male and female categories. The age-graded scores for these eight runners were the same in both categories, suggesting that cross-hormone treatment reduced running performance by approximately the size of the typical male advantage.
That reminds me of the swimmer Lia Thomas who placed 6th and 2nd before starting HRT. Raced against men after starting, which dropped her down drastically. Then when she raced against women she resumed being a top 10 athlete, winning her race (didn't even brake female records mind you, just won her race).
The study has some bias imo. For starters most studies I've looked at say 2 years is when the strength levels start to even out, while most measurements from this one are from a year. The major exception being a study from 2004 that only looked at mass not strength.
When this study does look at strength it very specifically looked at grip strength and leg strength (this is where I got suspicious of bias). Trans women have larger hands due to our skeletons being forged during male puberty, which could account for the differences in grip strength (easier to grip/more muscles being used when there is more hand to use). And as for the part looking at thigh and quadriceps strength: every cis woman I know has significantly stronger legs than they do their upper body and that is for both the ones that go to the gym and the ones that don't. It is completely possible (and not even mentioned which is where the feeling of bias comes from) that HRT has less of an effect on leg strength than it does upper body/core. If cis women who go through an estrogenized puberty have stronger legs than arms then it stands to reason that trans women would loose less muscle mass in their legs than their arms.
Edit: bias might be the wrong word here, maybe closer to an oversight than outright bias
Edit 2: found a more recent study that states endurance things like running and swimming level out by around 2 years, with most things level out after about 4 with the exception of upper body strength. Which is still declining in trans women past that point
https://academic.oup.com/jcem/advance-article/doi/10.1210/clinem/dgad414/7223439
So the 1 year that is recommended is too soon for trans women athletes to start competing, but for endurance sports like racing and swimming it should be fine by 2 years. Other sports may need more time, but also we shouldn't be delaying the lives of trans people for so long. We need to find a good middle ground because it's not like exceptional cis women don't exist in those same sports.
This is all also completely ignoring that if a trans women starts hrt before puberty then there is no real difference. So the real solution is to let trans teenagers transition.
I remember those same kinds people in high school saying "I'm not straight I'm normal"
So I'm gonna guess his response would be "I'm not cis I'm normal"