At long last, a unified theory combining gravity with the other fundamental forces—electromagnetism and the strong and weak nuclear forces—is within reach. Bringing gravity into the fold has been the goal of generations of physicists, who have struggled to reconcile the incompatibility of two cornerstones of modern physics: quantum field theory and Einstein's theory of gravity.
This is not really true. Lots of very well tested theories in physics came from math first, and then experimentation upheld them.
Einstein developed general relativity based on mathematical principles (Riemannian geometry and the equivalence principle) with little direct experimental input. And then successfully predicted the light of distant stars bendng around the sun.
Paul Dirac formulated a relativistic equation for the electron. The math naturally predicted the existence of a positron which was discovered years later.
Peter Higgs and others proposed the Higgs field to explain why particles have mass within the Standard Model, in 1964. It wasn’t detected in experiments until 2012.
Maxwell’s unification of electricity and magnetism led to the prediction of electromagnetic waves. 20 years later Hertz detected them.
Just months after Einstein published general relativity, Karl Schwarzschild found a solution predicting black holes. With no data at all! Sure enough, we’ve observed them and their effects many times.
Mathematics often leads the way in physics.