They should be sleep deprived the same way for it to be a real control group, at least in the context of "becoming a father". Otherwise it's just "being sleep deprived for 6-12 months has X effect", which is much less informative. We already know being sleep deprived for long stretches is really bad.
I'm pretty sure you can be father and have someone to take care of the baby in the night, your wife or paid nanny can do it, so omitting sleep deprivation from title is just sensational clickbait
Yes, so then that way you would know if there's something special about raising children that causes cerebellum shrinkage, or if it is just run of the mill sleep deprivation that causes it