I completely agree that those two are the relevant questions. So is there a good evidence for either of them?

All I found was anecdotal evidence that intelligent children of educated parents seem to fare better with unschooling than average children at school. And we would both agree that such evidence is irrelevant. (At best, it is evidence that unschooling is not completely destructive. But the claims in favor of unschooling seem to be stronger than that.)