It’s true that there are a lot of different theoretical proposals that serve as alternatives or extensions to mainstream physics: string theory, supersymmetry, Gauss-Bonnet gravity, GUTs, and much more. 

Many point to the success of our standard picture of reality, based on Einstein’s general relativity and the quantum field theory of the Standard Model, and (prematurely) dismiss all such alternative explorations. 

However, a tremendous amount of progress has been made simply by constraining and ruling out many such alternatives and extensions through data-driven experiments and observations. That progress is underappreciated, representing a huge achievement whenever it occurs.