For what it's worth, Wikipedia rather disagrees with you here...
OK, but I'm not relying on Wikipedia for my literary criticism. You only have to read HPL to see (as the Wikipedia page you linked to tells us) that "An ongoing theme in Lovecraft's work is the complete irrelevance of mankind in the face of the cosmic horrors that apparently exist in the universe". This is a pulp literary version of the same themes that were being written about by many authors in the early 20th century (influenced by developments in physics - especially relativity - and developments in biology - especially evolution). For a non-fiction and more Whiggish treatment, here's
a link to Russell's "A Free Man's Worship". Russell refers to "the world which Science presents for our belief" as one which is "purposeless" and "void of meaning". He goes on,
Amid such a world, if anywhere, our ideals henceforward must find a home. That Man is the product of causes which had no prevision of the end they were achieving; that his origin, his growth, his hopes and fears, his loves and his beliefs, are but the outcome of accidental collocations of atoms; that no fire, no heroism, no intensity of thought and feeling, can preserve an individual life beyond the grave; that all the labours of the ages, all the devotion, all the inspiration, all the noonday brightness of human genius, are destined to extinction in the vast death of the solar system, and that the whole temple of Man's achievement must inevitably be buried beneath the debris of a universe in ruins - all these things, if not quite beyond dispute, are yet so nearly certain, that no philosophy which rejects them can hope to stand. Only within the scaffolding of these truths, only on the firm foundation of unyielding despair, can the soul's habitation henceforth be safely built.
How, in such an alien and inhuman world, can so powerless a creature as Man preserve his aspirations untarnished? A strange mystery it is that Nature, omnipotent but blind, in the revolutions of her secular hurryings through the abysses of space, has brought forth at last a child, subject still to her power, but gifted with sight, with knowledge of good and evil, with the capacity of judging all the works of his unthinking Mother.
Russell goes on to articulate his conception of human value within such a cosmological picture; HPL is, in effect, casting doubt on human value - hence
cosmic horror.
Given that a principal function of religious belief and practice is to express, uphold, etc human meaning, purpose and value, I don't really see how a literary vision of a world in which the truth consists in
s the complete irrelevance of mankind in the face of the cosmic horrors that apparently exist in the universe can be described as a religious or theistic one.
(Of course, if by
deity you mean
being worshipped by (some) humans then the Great Old Ones are deities, in the sense that there exist cults of worshippers and so on. But in that sense a PC can be a "deity", as a PC can establish groups of worshippers. As I said upthread, when I talk about
deities in the context of a RPG world I'm talking about beings which are
actually deities - beings who anchor and integrate the greater cosmos into the lives and purposes of mortals. I'm doing imaginary cosmology, not imaginary sociology.)