Argument against considering them the same level of abstraction: HTTP and especially TCP stand on their own to do useful things (e.g. gRPC + every video game ever), so it's not necessary to understand HTML to understand and use HTTP. HTML and JavaScript can just be static files served over file://, even if most modern HTML/JS is delivered over HTTP. If you wrote perfect modern HTML/JS, you might never hit certain aspects of HTTP like 404s or 500s. You might be a DOM wizard but not have a deep understanding of 301s va 302s. You might understand nearly every HTTP header detail but get tripped up on ES6.
None of this is to argue that that a deep understanding of HTTP/TCP doesn't help write better HTML/JS, but they are separate things that can be considered separately.
I didn't say I considered http and TCP to be part of the same level, I consider parts of them to be part of the same level (e.g. the basic nature of requests, like the GP was talking about)
Full use of xhr needs some (but not complete) understanding of http and TCP because the abstraction isn't a perfect one, nor is it supposed to be.
However, full understanding of HTTP/TCP can be very helpful, even if not necessary.
None of this is to argue that that a deep understanding of HTTP/TCP doesn't help write better HTML/JS, but they are separate things that can be considered separately.