I don't know what the right answer is but I do kind of feel this desire for equal effort might be misguided. My sister wanted to spend her time raising kids. Her husband less so. That is decision they made together. It's no different than any other difference. He like working on cars. She likes knitting. She doesn't require him to spend equal time on knitting and he doesn't require her to spend equal time on cars. Why are children any different?

Further, many cultures, past in particular, seem to be very different in terms of parent involvement. To take an example from fiction, Harry Potter goes to Hogwarts at 11 years old. Yes, that's fiction but it's based on current and past cultures. It's still a thing in the UK for "elite" kids as young as 7 or 8 to go to boarding school, away from their parents. Kids in places too far for a public school are often sent to other cities, to boarding schools. East Asia & India also have famous boarding schools.

The point being, this idea that parents must be with their kids many hours a day until they kids move out of the house at 18 or 21 is not a fact of life, it's a cultural choice. I am from that culture and wish to spend as much time as possible with my kids. But I can also see it's a cultural choice, not some universal way things must be or else bad stuff happens.