Ah fair, I do see your point on a difference between existence and understanding. Though, some of the theories I've heard basically posit that gravity doesn't really "exist" in any sense that we have of it now, but is rather just an exposed slice of some higher dimensional reality that we can't experience entirely. But, to your point, something obviously exists there because it's measurable, repeatable, etc, so from that perspective nobody is questioning it's existence.

Also what came to mind was picturing Einstein doing his thought experiment where he was in an elevator at various levels of acceleration, and his observation that there was no way to tell the difference between the force felt from gravity vs. the acceleration. That to me feels a lot like quesitoning the "existence" of gravity! But I don't think we're really disagreeing, more were just operating with different definitions in mind of "existence."

Appreciate the discussion!