Turtledove is an interesting case study for both personal and literary criticism reasons. (And I'm not talking about his different kind of 'screw' scenes, or how his work gets worse as it gets longer).
As an artist, his parallel-filled, obvious divergence AH shows the kind of compromises you need to make to appeal to a wider audience, especially when you're doing "AH As A Genre" and not "AH As A Setting".
Personally, I came (just?) after Turtledove's crest. In the late 2000s was when I got into alternate history, and I mostly just found the relevant stuff on the internet itself. Turtledove was an author I read, and a lot of his books I liked, but he wasn't the entry-level bottom rung the way he's been described as for a lot of people. For another genre, Clive Cussler very much was this for me and cheap thrillers.
Since then, the bottom rung has shifted ever more towards Paradox games and, more frequently, people just jumping into AH communities online.