If you now answer that it's unfair that the person with naturally occurring higher levels can have it but those with lower levels can't "level" the playing field, well, tough luck. That's just the lottery that gives some people an advantage in certain sports. We all accept that some people are naturally tall and therefore have advantages in basketball. Or some people have naturally stronger VO2 max and thereby advantages in endurance sports.

The competition is how far you can get with the _natural state_ of your body, plus training. Not how far you can get as long as everybody pumps some substances up to a previously-agreed-upon threshold. Those thresholds are just the sad plan-B solution of anti-doping agencies if they can't directly measure doping substances and need to resort to measuring the effects instead. That actually disadvantages those with naturally higher effects.

Nobody would think of restricting maximum leg length, and as long as your legs are not longer than that it's fine to surgically extend them.