They contradict each other. Call that incomplete if you like. Newtonian physics gives accurate results in everyday circumstances. Go to any beginning physics class anywhere in the world, and the student begins with Newtonian physics--no mention of relativity or quantum mechanics. But does Newtonian physics describe all physical phenomena? No, that's why relativity and quantum mechanics were invented. But again those two new theories contradict each other. So the search is on for a better theory.
One could say they contradict each other. They are the best we’ve got though. Considering the strengths of each it might be better to assume that they agree on gravity being fundamentally misunderstood on a very basic level. The assumptions are wrong. If that means it’s ‘logical’ to invent multiple dimensions instead of rethinking the basic mechanism, then you would have to redefine the word logic.