I pretty much agree with what you wrote. That said, I think that GenServer/supervision trees are the pieces people should learn about, because in my experience they are great solutions in many cases, and I’ve yet to see a production which didn’t need a GenServer nor some form of supervision tree fairly early on in the game.
With a lot of hand waving, I’d say that GenServers are OTPs built-in building block for building responsive services, Tasks are the same for non-responsive ones, and supervision tree is the built-in service manager like systemd or upstart. In the past 10+ years of my backend side experience, I’ve worked on small to medium systems, and all of them needed all of these technical approaches.
So I guess my point is that while OTP abstractions can be misused (and they frequently are), they are also very useful, and in my experience very frequently needed. I’ve tried to provide some examples of both functional and concurrent design in my To spawn or not to spawn? article. In particular, in that fairly simple example I already use a couple of GenServers and Supervisors to separate the runtime activities, and I don’t think it’s overengineered.
But I ultimately agree with you that with the ecosystem evolving, there’s less need to write GenServers ourselves, since many common cases can be covered by 3rd party libraries, such as Phoenix, Ecto and others.
