When I last scanned film using one of the Pacific Image scanners the images were sharp in that it was clear that the grain was limiting the resolution. That was on fairly new film going back to the early 2000s so I don't know if that affects things or maybe the originals just weren't sharp.
As far as sharpening things I would look to using RawTherapee and play with the sharpening option there and try using
RL deconvolution and then playing with the Contrast by Levels sliders in the same general section, if that isn't enough you can go under the advanced tab and enable the wavelet tool and there I would use the contrast by levels as well as sharpening and edge refinement tools.
As far as testing to see if there is a problem I would go and send a modern exposed roll with a shot that has a super sharp image on it taken with a super sharp lens off of a tripod with more than enough light. So basically grab a 50/1.4 stop it down to f/8 use some ISO 100 film, really work to nail the focus off of a tripod during some nice bright mid day sun. If you can't get an image like that sharp then I would say there is an issue with the scanner.