Generally, a sysadmin has slightly different skills from a developer - they might code in a highly imperative style and always keeping the actual machine/system being targeted in mind, but I've never known a half-decent sysadmin who cannot write code.
If that's the term the market wants to use, fine. As far as I'm concerned, a senior sysadmin who can't write in a couple of scripting languages isn't senior.
I know a reasonable amount of sysadmin (all my computers run Linux primarily, I only keep Windows on for checking hardware issues, and a couple of specific apps I need to run once or twice a year).
I wouldn't apply for sysadmin jobs, because I wouldn't feel my knowledge is enough. I have however seen devops jobs that seem to match my skillset - developer with a bit more. I hadn't really heard of the term until I saw the job ad.
As to DBA; I can't help but feeling that the OP hasn't worked with "real" DBA's. That's a whole different ballpark and I've yet to meet a sysadmin or developer who can make even a passable DBA.
I've always thought the hierarchy goes: DBA -> Ops -> Developers. With the last two really about equals.
When I think about expected earnings, I would say your hierarchy is correct.