walrus
From using both I have more faith in the sealing lock nut to stop water than a hub.
I would say a hub provides a stronger mechanical connection as it has more surface area in contact with the enclosure and raceway.
You are correct the seal makes contact with the threads.
That is why I said they can be a bear to put on, I was using a 4" x 6" nipple between NEMA 3R enclosures and threading the sealing lock nuts on the nipple takes wrenches the whole way as the seal presses into the threads.
Once tightened against an enclosure no water is getting by.
The 4" hub on top of my meter socket which has been tightened with wrenches still lets water in.
Bob