@durin - had a thought, about the ongoing nature of our people.
In general going forward, those with low wills will have been purged from the gene pool, and that's probably helpful. More than that, though, it's now the case that every living person on Avernus (with the possible exception of those hiding out with the Sirens) has had the experience of holding strong against significant, direct demonic temptation. That seems like the sort of thing that might have been a significant psychological experience, and possibly worth a trait in and of itself. The psykers had it even worse, and might reasonably get a somewhat more potent effect.