I agree with your main point - a decent working knowledge down-stack really helps with network stuffs.

"nearly complete" strikes me as a whole lot of hubris though - I've spent almost 20 years at a career that can be summed up as "weird stuff with packets on linux", and the only thing that I'm certain of is: every time I think I'm starting to get a handle on this networking thing, the universe shows me that my assessment of how much there is to know was off by at least an order of magnitude.