Second, splitting a general role ("backend engineering") in arbitrary atomic skills doesn't make sense because there's no end to it. Backend engineering -> OS fundamentals -> Driver programming -> Hardware design -> Boolean logic -> Set theory -> and so on...
Third, all engineering roles have cross-cutting concerns. You do need some network knowledge to be a "backend guy"... but also to be a sysadmin, devops, etc.. It's not like all these roles exist in a vacuum and you're starting from 0 if you switch between them.
Finally, most people that think of themselves as experts in some role, language or framework end up in the "1 year of experience repeated 10 times" trap. True experts are also somewhat generalists too, because you can't built a tall knowledge without growing the base too (pun intended).
[1] https://www.bbc.com/future/article/20121114-gladwells-10000-...
