Oh, I know about ontological arguments. If we can conceive of a being greater than any other, then that being must exist or it would not be greater than any other, as St Anselm had it.

Problem being that my 'being greater than any other' is not yours nor anyone elses'. My 'being greater than any other' would have no interest in humans, would not welcome our worship if they noticed it and would have far more important things to do than 'take heed lest a sparrow fall'. Yours probably has different ideas. Do all of them exist? One God per person?

Perfection is as individual an idea as any other.

I volunteer at a Food Bank. It's a Christian-based one. They don't like my views, but they do appreciate my skill with a spreadsheet! Also my ability to persuade/bully shopkeepers and store managers to donate food which, while close enough to expiry for them to throw out, is still perfectly edible!