"With the creation of the Tetrarchy, at the end of the 3rd century, a stylistic break occurs. Imperial portraits then lose their expressiveness. They are hardly individualized, as if to underline the unity of a shared empire. In general, portraits are becoming more and more stereotypical and embody the imperial function rather than the wearer." Michel Amandry I agree !
This was certainly true for the 1st tetrarchy, but, in the west at least, seems to have rapidly reverted to more individualized portraits after that. The eastern busts, especially at Daia's mints, continued to be pretty generic though. It seems the generic busts are associated with the tetrarchy idea, and once the tetrarchy falls apart it reverts. Perhaps the east vs west difference is explained as those still considering themselves as part of the tetrarchic system vs those in the west (Constantine, Maxentius) who were out for themselves.
Well @Heliodromus has proven his knowledge once more. From the same hoard we have Severus II Obv:- SEVERVS NOBILISSIMVS CAES, Laureate, draped and cuirassed bust right Rev:- GENIO POPV-LI ROMANI, Genius standing left, holding patera and cornucopia Minted in London Reference: RIC VI London 59a, LMCC 4.02.016 Weight: 8.1g Diameter: 27.2mm BM Ref# 081