Mostly Harmless.
On
Lest Darkness - - -
You are the archtype of Hobbit's comment in the Anyone Help ID Books thread.
"I said we had members who were good.... "
A couple of cultural comments. When de Camp was writing the SF community as a whole was probably more cynical and less careful in it's religious skepticism than now. Due perhaps to leftism or techieness they were outside the much more common religious sensibilities of 1939. I am not aware of any of the period SF literature that involved religion as other than a cultural artifact, a delusion, or a hoax.
That's a minor disagreement. And as you point out deCamp is in fact in line with Van Loon, as popular a historian as there was in that or any period.
Rhetorical approval of slave revolts would also fit with the sort of attitudes of that time. That would be both modern and contemporary to his audience.
Your discussion of Belisarius takes me back to when I read Graves and deCamp as a kid (quite some years after they were written

) Thanks for the education.
It's odd that my comment was about a comment rather than the review. Matt, you really got the spirit of the book. "Competent Male's Dream", humor, even slapstick et al. All on a background that was probably Terra incognita to the large bulk of readers. I was a nerd who read Graves - but was an exception (and for that matter, read deCamp first.) I think you overplay the lack of explanation for the time jump and incongruities, but that's my bugaboo. Rather than invented pseudo-science I much prefer that something just happened.
As you mentioned, I remember thinking that his pickup of language was improbable. But I was a teen who had struggled getting along in a foreign language country. So even that might have gotten by most readers.
As usual, very good job.