"If strength, resting heart rate and muscle type is a factor in darts why is it a sport dominated by fat middle aged generally unhealthy men?"
Because even, to use your own words, fat middle-aged generally unhealthy men have the physical attributes and have honed their skills so that their own lack of fitness doesn't mean they lose competitiveness against other male people.
However, even a male in the bottom quartiles for grip strength for example will have a strength that is higher than most female people. I believe I read something like higher than 90% of female people. Hence it is only an absolutely exceptional female that will have higher strength in grip than the weakest group of male people.
You don't seem to understand the degree of differences here.
So, do you laidbackguy understand then a mediocre male person is being rewarded for being mediocre compared to the best male competitor by competing in the female category? That just because you don't understand that the chances of that male beating an elite level female competitor makes this undoubtedly unfair competition. This is not an elite level male competitor taking the place of an elite level female competitor. It is also a male person who has deliberately limited their performance level through their own decisions.
It also comes down to category boundaries being ignored to allow someone from outside a protected category to compete. What other category would you be happy to have ignored because someone 'identified' into that category?
Should a sighted person compete with visually impaired athletes if they identify as partially blind?
Should a 25 year old compete in the under 14’s if they identify as a child?
Should a 25 year old compete in the over 85 year old Masters category if they identify as 86 years old?
Should a professional athlete compete as a novice?
Nothing to worry about, those who identify into those categories don't have any advantages in your opinion.
All because why, laidbackguy? Because people such as yourself don't understand the physical advantage of males and are prepared to ignore those male physical advantages and the discrimination that have prevented female competitors from achieving their full potential as well?