It is possible to de-anchor salary expectations from your old job. You just need a good excuse. Moving to an area with a high cost of living -- like, say, Silicon Valley -- is a good excuse. So is "I was working for a startup and most of my job's expected value was locked up in equity".

"My last company systematically underpaid everyone" isn't, even if your last company systematically underpaid everyone. It may be true, but the people interviewing you won't usually bother to find out, and it sounds bad either way.