The presence of a biological father in the household as a protective factor for children's development is long established. That study has been repeated many times... presumably due to skepticism of the prior conclusions.

I am unaware of any studies designed to ask if the presence of a biological mother in the household is of any developmental value to kids.

Apparently some questions are, in fact, too intuitive to study.

But to the point of this, I still find it surprising that a researcher was curious if a parent is happier when their child is thriving.