I can only agree with all what you wrote, though Chambers and Derleth cannot really just be dumped in the same bag, one being a prequel, the other a sequel of Lovecraft work.
Your points on derleth are very true (including the one in the edit). Though, except for the passage with Derleth obsession of telling apart gods and ancient ones, I found that the lurker was really nicely designed (at least to my taste).
best


