Alright, I know I should not step in to the mess that is the gender wars. But here I go anyway..
The thing with Doc Q and Law imo is,
Because Law is genetically Male, and got turned into Female without his consent, it can be seen as a "disease" or "defect". Law his whole life has been a male. So getting turned to female suddenly in the middle of a battle is gonna affect him and his performance in battle. I am sure oda just thought " This would be a cool power for doc q" And included that. He probably doesn't think about gender politics and nuances, probably.
Don't ban me, or do. Whatever. Idc.