So for those of us who are neither philosophers or educators but have an interest in teaching the craft, and discussing teaching the craft, how would we proceed? Or are we doomed by lack of a solid theory of paedogogy?
Not doomed. Individual people will be able to proceed informally with some skill, and perhaps even get a bit better if they're really interested in doing it well. But to "git gud", you need a robust system of practice you can insert yourself into that simultaneously teaches you how to teach while also teaching you what to teach. Funnily enough, play-based education methods for children IRL have already solved this problem, using games to teach teachers how to teach children using games.
What I would say is right now we're in a situation where the majority of successful paedogogy mostly relies on the heroic efforts of individuals who have cultivated their talents both as referees, and as teachers, and who then, mostly through chance, encounter interested pupils. Part of the shift to a superior mode of transmission is to regularise and broaden the methods of instruction and the methods by which people are inducted into them.
Streaming is doing a bit of this - it's providing people with an impersonal example of a certain kind of good play that doesn't rely on them sitting down at a table with a great referee who eventually teaches them their secrets - but it's not revealing the underlying structure of those sessions or how they're produced, and it's mostly focused on a very particular kind of play (showy, dramatic, primarily about what Tuovinen would call "princess play, not too crunchy or mechanically-focused, etc.).
OSR blogging is another tool - part of the OSR's success is not so much about its actual position on anything in particular and the appeal of that position, but about how accessible and paedogogically-oriented it is, especially around technique. You can learn "to run a West Marches game" way more easily through forums and blogs than you can learn how to run a traditional "silver age" Dragonlance rip-off. The OSR focus on technique is one reason you see trad gamers adopt its terms and concerns sometimes, even if they don't want to. The story games crowd is in a similar spot in terms of sophistication of transmission, and that's probably why the two groups seem like the two most important scenes in RPGs outside of the swollen convulsing mass of 5e newbies.
I'll admit to a somewhat irrational and unempirical love of text and diagrams, so while I don't think it would be a complete solution to the problem, I think WotC should put out at least one book covering basic skills. This would range from establishing a standard visual grammar for hand-drawing battlemaps and dungeon maps, to the assignation of roles like mapper, caller, timekeeper, initiative tracker, along with lists of responsibilities and checklists for new DMs to hand out (advice on drawing up calendars and maps would be good too). It could also include advice on using mind maps, relationship maps, timelines, etc. to plan a campaign, and how to stage rolls to generate maximum excitement and engagement at the table. It could include a list of sample social conflict scenarios for DMs to consider with advice on inobvious features or solutions. etc. etc. etc. There's tons more that could be in there. I would think of such a book as the true "Dungeon Master's Guide" even if it ends up being called something moronic like "Melathaur's Guide to Lost Lore".