For film negatives this scanner will get about 2300 dpi according to [0]. A DSLR with 24 megapixel will get the ~4000 dpi form a 35mm negative in a fraction of the time.
A 4x5" negative takes 33 minutes to scan with 2400 dpi. In this time I can make several photos and stitch them together do some spot removal and will get a better quality.
The DSLR+adapter solution does sound more convincing to me, with the right lens, right sensor and settings. Correcting distortions should be a tractable.
One problem with many flatbed scanners (not all of them and not the film scanners) is that they illuminate the film/object from the same side as the sensor, so the light has to travel and bounce more, creating more chances of stray light.
A 4x5" negative takes 33 minutes to scan with 2400 dpi. In this time I can make several photos and stitch them together do some spot removal and will get a better quality.
[0] https://www.filmscanner.info/EpsonPerfectionV700Photo.html