Any strategy is most likely still useful as long as it is done properly like everyone is mentioning.
Remember that the point of a PBN is to just mimic a normal website. So, the basis of the utility of a PBN will always be useful. It is just a privately created high authority site. If Google doesn't notice the footprints then they will see what they see for all other sites, just a decent and informative site.
SO, yah, PBNs are useful. They were, are, and will be useful as long as google improves rankings based on backlinking profiles.