Robert Silverberg is a sometimes a good alt-history writer, Christman has praised him. When he's at his best he's drawing parallels between divergent ruling classes and our own. He's at his worst when he's getting deep into the idealism, like his alternate Rome that survives to the modern day because Christianity was never invented, and so the western and eastern Roman Empires never fought one another. You got it right. Alt-history guys usually don't understand materialism.

Kim Stanely Robinson wrote a pretty good alt-history novel, "Years of Rice and Salt." The premise is the black plague kills 99% of Europe, so it's a world without white people. So the whole world is split between various Chinese and Muslim states. It's a good novel because it's from the perspective of two people who keep getting reincarnated. There's a chapter where one of them is a tiger.

I wouldn't call him "alt-right adjacent". More just your run of the mill anti-communist shitlib who may or may not vote Sanders. The fact that he has far right fans is more just that the specific brand of low-effort althist gruel panders to the kind of audience who are susceptible to it otherwise.

Side note but there's an interesting in-progress Drakaverse revolution forum quest (ie, alternate history where repliers can influence it as its written) by Marxists on SV.