I agree it's incredibly important to dig into layers under (and over) the one you're working at! I'm very grateful for the experience of building a simple unix-like kernel and a simplified TCP & IP implementation as school projects. And I'd encourage anyone to do the same with HTTP 1 or 2 or 3. The difference is that no one thinks that their educational/toy TCP implementation is suitable for production use, while people do seem to (mistakenly) think that about HTTP.
(I'm not agreeing with the author, just pointing out why he might care about the ability for an individual to implement the protocols the web is built on.)