I think there are a couple points here.
It's inevitably the case that people who have sorter rather than longer careers will have on average a different kind of career. That's not necessarily a bad thing. There are a variety of reasons people might take such a break.
It's increasingly common for people to have major career changes in a lifetime.
Many people live long enough, and in many cases have a long enough working career, that they can have several careers, or start late and have a full career even beginning at 30. The fact that we look askance at this is mainly down to prejudice, not any real assessment of people's skills.
Many, many, many people have jobs rather than careers.
Even while working, one or both parents typically need more flexibility in work commitments in order to manage the demands of family life, which often translates to a less demanding, and highly paid, job. This is especially true if one parent has an especially demanding job.
One way or another, someone in society is putting in the time to take care of the kids, parent or not.
The fact that child-rearing within the family can't somehow be worked into this, for men or women, isn't really about fitness to work or any intrinsic demands of work.