Most of these jobs would never get posted in the first place, you need to already be a known entity with these groups/be trusted before they let you close to the mainframe. Have a friend in one of these roles currently, ~10hrs/wk, remote, 6 figures.

People in these roles don't want to draw attention on their sweet comp packages which is why you won't see them crow about who/where they work.

Those do exist, but as far as I'm aware the most common structure currently is that it's mainframe consulting companies and their consultants that command those salaries. Anyone in an actual employee position I've never heard of making above 100k/year.

I have a friend who went from being the form to the latter and immediately doubled his salary, despite the consulting firm making it clear that he was at the bottom of the totem pole, despite his being 5 years or so into mainframe work.

To be fair I'm in this position but it's with a small company that aren't exactly regularly hiring.

I suppose the point is, these jobs exist but it's quite hard to replicate as it's not common with large firms that are regularly hiring.