You are correct that the drivers are not tour guides, however, the Joe Banana company will arrange private guides if requested. We had a guide for the Vatican and Pompeii that JB arranged for us. Of course, we tipped both the guides and the drivers.
Our driver for Pisa and Lucca was local to Lucca and he gave us suggestions of what to see and where to go when dropping us off, which was appreciated.
Our Naples driver lived in the hills around Sorrento and offered nice stories and information about the area. We didn’t go exploring on this excursion because he took us directly to the farm/restaurant and back to Pompeii and back to the dock.
In Rome, the driver took us to the sites we wanted to see and waited by the van while we spent time in each area. Once we reached the Vatican, he left with the van after we met up with the guide and came back for us a few hours later to take us back to the port.