I certainly have seen more conduits open at compression fittings than set screw ones. I think electricians also install set screw fittings more reliably than compression fittings. It is easier to be satisfied the raceway is fully inserted into the fitting on set screw fittings. In compression fittings the ring often interferes with an easy and reliable fit. Sure electricians should be ensuring proper insertion but removing as many possible errors in the choice of fittings can help. Yes i know more than a few sparkys that are remiss in tightening set screws too. This spec has been on the books for so long that I thought that compression fittings must have come to market at the time when EMT fittings were installed with a dimpler. Even in concrete I prefer set screw Steel fittings. As for fault return path and lower impedance? I expect the compression fittings might be better the first fault but any second faults would be about equal after all the spot welds are made.