As long as neither spouse is sitting on his arse while the other is working hard and gets no free time, it's all good. Free time should be divvied up fairly in any relationship.
If one spouse is living a great life with lots of leisure and looks forward to each day, while the other spouse wishes they were dead, that's a problem. If you love your spouse, you wouldn't want them to be so miserable. And if you love your spouse and marriage, you'll want it to last. One spouse getting burnt out is not sustainable.
And yes, the early years of a marriage are the hardest. When you have 3 (or more) kids under 5. Until they can help out, it's all on the parents. Each child does mean more work (not much more money, as claimed by MIT and other Jews -- but more work, yes) but they don't carry their weight at all.