[manquer]

By that logic I as AP dev should know systems programming and OS. A systems programmer should know kernel development ? A kernel developer should know assembly and microprocessor architecture?

Everybody has at best little or shaky knowledge of underlying abstraction. Yes it helps to know more, but is not really practical to expect that knowledge as the minimum required.

[dilyevsky]

Yes you should have at least some knowledge of architectural principles and design of an api layer you directly depend on. How is that not just common sense?

[jackcviers3]

Yes. You should know one layer of abstraction below the one you are using. Always. Because everything leaks, and eventually you have to fix it.