I like the line "This reduces the study of history to a collection of trinkets", cause I've seen a lot of that. To give one example, a lot of sports AH I've seen involves mostly shuffling OTL player and team names/outcomes around (which requires only basic knowledge of those names) instead of trying to fundamentally change the game (which requires a deeper knowledge of the system and what a change would bring).
It's a great line, and seconding that I too rather liked it. Being a member of Alternate History Online Facebook group myself, I've seen a lot of what you talk about @SpanishSpy on there. I agree a lot of it is down to the way history is taught and also the way much of the genre is written. As a writer myself, I can vouch for how much learning not to think that way, and to get into the specificity helped in terms of research and writing. The question is how do we help others to learn that without either losing our patience and/or chasing them away.