I would say I have a pretty good understanding of Ethernet, IP, TCP, and also HTTP, having written implementations of that full stack several times -- including pretty sophisticated ultra-low-latency tricks.

HTTP/2 implements multiplexing on top of TCP, which is just plain stupid. TCP is not meant to be used for this, and doing this is actively harmful; the correct thing to do is to establish multiple TCP connections. That sort of thing is not surprising since most of web and cloud tech is all about re-implementing low-level components on top of inadequate high-level abstractions.

The main reason to use HTTP/2 is simply that when a server provides both 1 and 2, the backend quality will typically be much better on 2.