@ByNimbleCrow the question of the mental load only arises when you have children. It really isn't a thing before then (and if it is, you're a fool with a simple recourse).
Birthing a child, caring for a baby, maternity leave - all this will change your life and outlook. Babies inherently need their mothers when they're born. After the first few weeks, dad goes to work and is out the house 60 hours a week. You become the expert on the baby, on top of the fact that you're the only one that can feed him anyway. You're home, so you may as well do some laundry and food shop. You spend all day with baby so you may as well buy his clothes, know what nappies he needs, when you run out of nappy cream, you're there for his first meals when weaning so you know what foods he prefers etc.
By the time you finish breastfeeding and go back to work, these roles are entrenched.
Yeah, I could choose to go back to work when baby is 6 weeks and for dad to stay home. But it's taken me 7 months to start to recover physically from pregnancy and birth injuries and pumping milk while working full time would be incredibly difficult, so me going back to work early is still harder purely because I'm a woman.
And that all makes it inherently a gender issue, not just a relationship issue. The majority of women out there are not talking nonsense.
If you're in a good marriage with a good man, it should slowly go back to 50/50 as children become older.
But setting boundaries is incredibly difficult as it affects your child's wellbeing. So you carry on, as your instinct to put your child first does not go away. Sure, you can divorce. But I don't know many women who want to be away from their child for significant amounts of time, especially if they spend that time with someone who has proven himself to not put the children first already!