I tend to think the one finger per fret is something that bass players have inherited (for want of a better word) from guitar players. One finger makes sense for most guitar runs, but the spacing on a bass can make that very uncomfortable. For my part, when I was just learning to play guitar, OFPF wasn't a thing and I learnt to play in the most comfortable way, which was predominantly index, ring, pinky (it fitted the box version of a minor pentatonic). When I jumped ship to bass, I just carried on this way without knowing that it was a variation of the Simandl technique. I use OFPF for exercises and warm ups, but I'm not conscious of what finger I use when playing actual songs, just what works and gets me there in the most comfortable and efficient way for me. During lockdown, I did woodshed a lot of OFPF and manage to give myself tendonitis! The times I have played upright bass (a friend has one), my dodgy Simandl seems to work fine, as do the patterns that I'm used to on EB. I'd love a DB.