One tangent, I believe sev-0 is actually "critical" (at least as how I'm used to reading it), and the higher you go the less critical something is.

IMO as a github-watcher, I think they changed their definition of what constitutes a sev-0 between sev-1 for the better. In particular, they had a few "sev-1"'s around the turn of the year that would be classified as sev-0's if they happened today.

Pre-4/22 GitHub sev-1 was a normal SaaS company's sev-0, imo. So I think their new system is more reflective of reality. My guess is that a few of their big customers bullied them to have more accurate SEV categorization.