Queen - The problem is not just testosterone levels.
Men have about 10-20% greater bone density than women.
Men have on average 36% greater muscle mass than women.
Men tend to have approximately 40% greater upper body strength and 20-30% greater lower body strength than women.
Men have larger lungs and greater lung volume, which leads to about 50% greater lung volume per unit of body mass than a woman of the same size
Men have physically larger hearts (about 10-15%) than women, and so have greater cardiac output leading to greater endurance.
Men have about a 10% higher erythrocyte count and a higher hemoglobin level, which leads to a higher oxygen-carrying capacity, which also leads to a higher endurance
Men produce more erythropoietin than women and also do so at a faster rate, leading to faster production of erythrocytes at altitudes
Men produce more clotting factors and have a higher platelet count, meaning that they heal faster from wounds inflicted during sports.
Source: any physiology textbook.
Taking estrogen downplays a few of these advantages but it doesn't change the person's bone size, lung size, heart size, erythrocyte, hemoglobin, or platelet count, or the amount of muscle mass that the person had before taking the hormones.
The argument that estrogen makes the person weaker is false because we are talking about an athlete who is training, right? So it isn't as if the muscle that they already have is going to atrophy - the estrogen is just going to make it less easy for them to build new muscle as rapidly.
(The author of this post is a scientist in a related field.)