Morrison said he would create a character that would be Jean's own personal archenemy/rival.

So if Sublime were waiting for Phoenix/Jean Grey for 3 billion years, then he is definitely a god.

Remember, Claremont referred to Jean in Wolverine 125 as an archangel made flesh. The caption said the woman is far more terrifying than the celestial raptor that is her namesake. She is the spark of fire that gave rise to creation. She is the spark that will ultimately consume it.

So Morrison is just establishing what Claremont already said, Jean is the physical manifestation of a god, the Phoenix.

Sublime appears to be an avatar of a different god.