Mostly, I've read people's qualms with Dye sub PBT is that it "bleeds" a little, making the letters "fuzzy" This has not been my experience, though I am by no means an expert. I have only one IBM 'board, 1 unicomp, some SP,and one cherry (all Dyesub PBT). In all cases, the legends look pretty good, though some few are a bit "faded" looking on my grey unicomp keycaps.
I have read that the reason for Dyesub variation is that as keycaps are created, they get more and more fuzzy-looking until the tooling is replaced on the dyesub machine. Perhaps I've gotten lucky thius far?
Given Imsto's "3d" PBT dyesub accomplishments, I'm unconvinced that modern techniques will render PBT legends any less "sharp" than doubleshot. This is especially true looking at the detail in the portal round1 keycap set.
---
mr626, might I recommend switching to PBT?