The rules of grammar are not divine revelations, they are rather
developed huiman practises. To speak of the holy one with a capital 'G'
rather than a little 'g' probably came out of that faith conviction that suggested that God was the infinitely real creator of the universe and therefore worthy of that act of ultimate respect called worship. It was at first probably little more than an expression of the human desire to praise the almighty one in exchange for divine protection.

When we refer to deities other than our own our rules of grammar
suggest that we use the little 'g'. That habit was clearly designed to show our scorn and to express some levels of negativity, e.g. 'the gods of the Olympus'.

My sense is that the upper case 'G' suggests respect and so I favor it. I would, however, use it when referring to whatever is regarded as that which is ultimately holy in every religious tradition.

John Shelby Spong