You can disprove my statement by naming something gravity does other than add a shape to spacetime, if you want. Saying "I think you're probably wrong, but I just can't say why" is not an argument.
But, that aside, the idea that gravity is spacetime is really just the theory of general relativity and that is clearly not the final word on the subject. Other approaches to gravity may admit alternative ontologies.
Again, I'm not trying to prove or disprove anything. Just saying that you are kind of oversimplifying an open scientific question.
I myself have many 'unproven' things about Physics, that I believe, with a high degree of probability (near certainty). Dig thru my past posts for lots of them. For example, I believe Minkowski Space is indeed itself emergent. I think our entire universe exists on the "surface" of a 3D Event Horizon (manifold). I don't believe in the Big Bang, because our reality 'formed' not from a singularity (exploding out), but like a Black Hole (falling in). So I'm open to lots of ideas, but just pointing out the what we currently know as General Relativity, isn't even that complex, and is just about a shape (curvature/tensor) at every point in spacetime. It's all we've "proven".