That was an interesting hypothesis, and I agree with you to a large degree, however my argument was not based on the denial of spirituality, maybe I should have worded my post slightly better, the problem I had was ascribing a supernatural phenomenon to spirituality, spirituality can in fact be induced in the human brain, there has been experiments carried out by; Michael Persinger in neurotheology.
Taken from Wiki title "God helmet" - Persinger uses a modified snowmobile helmet or a head-circlet device nicknamed the Octopus that contain solenoids which create a weak but complex magnetic field over the brain's right-hemisphere parietal and temporal lobes. Persinger reports that at least 80 percent of his participants experience a presence beside them in the room, which they variously say feels like God, or someone they knew who had died.
Also indeed you are correct, spirituality have indeed played a role, art, music etc. it has some kind of basic dependence on preternaturalism, but yes some art is based on mysticism/spirituality but that does not necessarily mean it had to be dependent on mysticism/spirituality or mysticism/spirituality was a prerequisite.