The older, more foundational problems were getting automated back then. Now that they're solved problems, and combined with more and more people running large and/or virtual infrastructure, a new problem domain exists around spinning up machines and deployment.
The current coding investment is infrastructure because it's the current pain point. In a decade (or whenever permanent solutions exists for infrastructure) the current way will be considered "by hand" and operations coding efforts will just move onto whatever problem is only visible now that infrastructure is no longer a time sink.
You can say that some ops is just admins running already existing software and operating everything by hand, but there will be admins doing exactly that in a decade too.
Then dotcom happened and every kid with a Linux box in their bedroom put themselves about as a SA. And in the 10s people think SAs who code is an amazing new invention.
And back in the 60s, IBM had "systems programmers"... Same thing.
The big difference I see in devops is that people started taking system management seriously enough to do first-class development rather than an afterthought.
I still am, but the "DevOps Movement" is here to point out that this artificial dichotomy is considered harmful.
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.
Nothing you described is outside of the realm of what your typical linux admin does. I don't have to be a senior python dev to do my job, and I've managed 5500+ virtual machines by myself (puppet/chef, bash, some python, persistent data/object storage).
Agree with the author; just shoving more hats onto less people.
A DevOps can expect a bigger salary, while a company hiring one can expect way more productive candidates than if they asked for only ops.