Severity went something like this (sometimes the numbers flip which always confuses at least 20% of the team about whether things are almost normal or people are hunting each other for sport).

1: data loss

2: some workflows blocked

3: some workflows unavailable w/ workarounds (ie other routes)

4: Everything else except

5: Irritations

Having a UI break but the underlying functionality is still working is not good but people can still do their jobs, if more slowly. It's important to classify these separate from S2 and S4. There is urgency but don't panic. Go eat lunch or have your planning meeting, then go fix it. If data is getting lost ain't nobody doing nothin' until we figure it out, and then some people can go back to work but don't interrupt the people still working on it.

I think the problem is that so many metrically dysfunctional people, to the point of cliché, have rationalized that an S2 means that only 20% of our customers can't do their jobs so we are degraded but still working normally, when really a yellow status should be at S3, while S2 should be at least orange although those affected will be upset that it's not red.

Over time that 20% will shift around to most of your customers. Eventually several times, and then you'll wonder why everyone is talking trash about you on HN. It's not like that many people were affected!