It's not just strength, bone density and all that.
Women have breasts with the sizes not of their choosing. Some are less cooperative to sports than others e.g. Simona Halep who had breast reduction.
Those born male don't get periods. Can these affect training? Of course and studies back that up.
Children. Those born male can procreate without any effect on their sporting career. Women have to factor this in. Do you risk your unborn child to continue competing? Do you take a year or whatever out and then try and regain that peak?
Even if you want to, studies also show that women athletes especially those at the top level's lifestyles are likely to decrease their chances especially in sports where heavy dieting is likely (MMA and other combat sports tend to require weight cutting for example)
Hardly a level playing field.
Also, how would you deal with someone born male , identifies as female, wins the fame, the fortune and everything that goes with it, retires and then reverts to the gender of their birth sex?
God, the Williams sisters, amongst the greatest tennis players ever, said they could beat any male "outside the top 200" but then lost to the male player ranked 203.
Live how you want to, but some things need to be demarcated on sex grounds, not gender.