The Lex Fridman podcast has an interview with Cumrun Vafa. Going to the section (1:19:48) – Skepticism regarding string theory) where Vafa answers the skeptics, he has just one argument for string theory as a predictive theory: it predicts that the number of spacetime dimensions is between 1 and 11.Vafa also says that string theory "post-dicts" gravity, because both string theory and conventional wisdom predict a spin-2 graviton.
I am not sure this means anything. A spin-2 particle could be a composite of two spin-1 particles. Maybe the conjectured graviton is such a composite. If so, string theory does not help.
He also said string theory tells us about possible universes. It allows examining a universe where electrons are 1020 more massive, and gravity is stronger than electromagnetism. If so, then black holes would not evaporate. We believe black holes evaporate, over trillions of years, so that explains why electrons are so light. Or so he says.
Vafa is asked about Einstein's greatest accomplishment, and says special relativity. General relativity is more complex, but is largely the consequence of special relativity and Riemannian geometry.
Vafa mentions, and dismisses, that it was the 1907 idea that gravitational acceleration is just like other acceleration. I think that may have been his best idea. Yes, it is obvious, in retrospect, but nobody else at the time noticed that gravity would affect time.
But special relativity was not Einstein's discovery at all. Vafa specifically credits Einstein for saying that the speed of light was constant, but I think the record is fairly clear that Einstein got that from Lorentz.
Vafa is a physicist, not a historian, but most of his argument for string theory was a series of historical anecdotes about physics discoveries of the past.