Similarly if a group of tourists gets lost in the jungle we don't call that a study of prehistoric tribal life.
Of course, don't we all? It would be much more useful to have data on what remote work will be like in the future (i.e., when kids are in school/daycare).
There is something interesting about knowing the pros/cons of what happened during the pandemic, but most of the time research is done so that the conclusions can inform future decisions. Here, the future decisions about WFH would benefit from disentangling the WFH aspect from the COVID-induced remote school aspect.
One way to accomplish this is to assume that all workers who have kids (and lost productivity as a result) would have had the same productivity gains of people without kids. There are probably smarter/more nuanced ways to determine the global pros/cons of WFH in the future.
Your comment only tells me you wanted a different study than the one they did.
Asking what happened in the real world, including in a range of work situations, is a very interesting question to ask.
Looking for/at the delta between optimal work-at-home and the office would also be interesting, for different reasons.