Well, there's lots to say here. I don't think Lovecraft is a great writer either. He doesn't include enough dialogue, for one thing. "The Call of Cthulhu" is probably the easiest and most informative of his stories, as far as cosmism goes.

I'm sure cosmicism can be formulated along the same fallacious lines as theism. Schopenhauer's negative pantheism comes close to that. All you have to do is project a deity but think of him in negative rather than positive terms. That would be a mirror reflection of theism.

But Lovecraft doesn't do that. He personalizes the universe's indifference and amorality in the form of the superhuman aliens and monsters in his stories that mock our sensibilities and vanities. Those aliens are to us as we are to ants.

Cosmicism needn't presuppose theism in any sense. What the cosmicist does is play with that science fictional projection, with positing superpowerful beings in nature who effectively prove that the universe doesn't care about us one way or the other, that we don't amount to a special, favoured species. It's just a dramatization of the existential implications of atheistic naturalism.

Your criticism is pretty much an ad hominem that overlooks the crux of the matter. That's largely because you concede the cosmicist's main point, that we're not cosmically crucial. You'd add that "consciousness" is, but that's not to say that human selves or societies matter to the rest of nature.

The question of whether something is significant depends on the standard or expectation. The cosmist takes naive theistic, anthropocentric religion as the standard, and shows how we're insignificant relative to that standard. We thought we were more important than we really are. That's what scientific and philosophical progress is supposed to show.