That just sounds like an experienced developer. X Y and Z could be Bootstrap, React and Angular. In that case you have an experienced front-end developer. In my view a full-stack developer is somebody who can write front ends, middle tier logic and design and use databases efficiently. In various phases of his career he should have worked specifically in each of these areas in depth. My view also includes the idea that a full-stack dev should understand how computers really work and should be able to spec a server/VM for a specific purpose. There are not many of these people out there. Heck, I was shocked 20 years ago at how few devs that seemed like nerds to me didn't even know how to take apart a desktop and diagnose a problem. Maybe I'm just an old guy and should worry more about the kids on my lawn.
I totally agree, that's exactly what I had in mind, X-Y-Z being a broader areas, not just a framework or a lib. For instance, I worked (in the span of now almost 20 years) on back-end, front-end, DBA and linux admin positions, and I'm not counting in that all the C++ and Delphi desktop programming that I did as a kid. This gives you a wider perspective on how things operate, and I find it very helpful when consulting clients on sys architecture, since I know how hard is to implement something in any part of the system and can plan for that ahead.
