I think you misunderstand how physical theories work. All physical theories we know have free variables that need to be fixed before being able to make any nume

I think you misunderstand how physical theories work. All physical theories we know have free variables that need to be fixed before being able to make any numerical predictions. In classical electrodynamics it's the permittivity and permeability of the vacuum. In Newton's theory is G. In General Relativity is G and \lambda. In QED is the fine-structure constant, \alpha. And the Standard Model of particle physics has 20 free parameters that have to be set by hand using input from the experiment before being able to use it to make precise numerical computations and having any predictive power. If you don't fix these inputs you don't have a theory, you have a family of theories and you cannot discern which one is the correct one. On top of that, Quantum Field Theory (QFT) the "theory" (continue reading to see why the word theory is a misnomer) that underlies the Standard Model is not constraining enough and you still need to pick the right gauge theories that model our universe. So QFT is better understood as a framework, from which we build a model of reality by hand-picking some theories that seem to suit our universe, then we fix their free parameters using experiments and only then we can predict everything else. String Theory is much the same as QFT in this regard. It's a framework for building physical theories. It arguably has less free-parameters (it has only 1), the string tension. Buy you still need to pick the right models within the framework, here again String Theory is arguably more constraining but you still have an immense amount of options, commonly referred as the String Theory landscape (or vacua) and relate to how you compactify the extra dimensions. So if you applied the same criteria to Quantum Field Theory you would come to the conclusion that is "an interesting mathematical model" but a "useless physical theory". Disclaimer: I studied Theoretical Physics. I do not work in academia or in physics, for that matter. My sustenance does not depend on money flowing into High Energy physics.