Does the pay gap even exist for same-level positions? I always thought it was basically comparing (sum male earnings)/(total males) to (sum female earnings)/(to

Does the pay gap even exist for same-level positions? I always thought it was basically comparing (sum male earnings)/(total males) to (sum female earnings)/(total females). If the pay gap actually existed for same level positions, and was the 83c per dollar as is commonly quoted, why wouldn't there be all-female firms, paying their employees say 90 cents on the dollar, such that their overall payroll costs are much lower for the same quality work as a workplace with mostly males. Shouldn't that company be able to outcompete other companies? If group A is more willing than group B to sacrifice their health and relationships to improve their value at an office, how can groups A and B ever be equally represented beyond entry level positions?