FWIW, there are ample counterexamples of startup founders who have had young children and done very well on both fronts. For example:
All but one of the Fairchild Eight had young children while founding Fairchild (and the modern Silicon Valley).
Jan Koum had two young children while founding WhatsApp.
The Zenter founders both had young children during YCombinator, and ended up getting bought by Google.
It can be done. I doubt anyone would consider it easy, but the data certainly doesn't a blanket claim of "You're not spending enough time on your start up AND you're not spending enough time with your family."
You didn't list any counterexamples, or at least we have no way of knowing if they are counterexamples. You've listed a number of examples where the startup founders had young children while successfully growing their companies but we have no way of knowing whether they were equally successful on the parenting front. Perhaps they sacrificed their parental responsibilities to achieve their business success.
All but one of the Fairchild Eight had young children while founding Fairchild (and the modern Silicon Valley).
Jan Koum had two young children while founding WhatsApp.
The Zenter founders both had young children during YCombinator, and ended up getting bought by Google.
It can be done. I doubt anyone would consider it easy, but the data certainly doesn't a blanket claim of "You're not spending enough time on your start up AND you're not spending enough time with your family."