Right, but this mystical concept of God as the impersonal, transcendent ground of being is consistent with atheism. What the atheist objects to is the personifying or idolizing of ultimate reality. The personification of God is due to exoteric religions, not to atheists. Atheists object to religions that are transparently silly and self-absorbed.

The kind of neo-platonic mysticism you've outlined here isn't silly, which is why it's largely consistent with atheistic naturalism. The ground of being looks a lot like the gravitational singularity that might have given rise to the big bang.

But you muddy the waters when you speak of a "universal manifestation of God as a person." Why should that manifestation or symbol be universal or so important? Spinoza's pantheism is more consistent in saying that the transcendent ground or substance simply has infinite properties, and none is inherently more important than another.

We're the ones who prefer personifications because of our vanity, not because God is inherently more likely to appear as a person than as anything else. God might turn himself into a person to communicate with us, but that still wouldn't make that incarnation metaphysically crucial. The contrary presumption would be that because we're so important, so is God's best mode of communicating with us. And that kind of anthropocentrism would start to look silly.