Just because the math is valid doesn’t mean it applies to anything in the physical universe. Until and unless string theory can ever move to the experimental phase, it’s a great exercise in mathematics.
...and when you look at the explicit predictions that have come out for the masses of the mesons that have been already discovered, by using lattice techniques, they differ from observations by amounts that would be a dealbreaker for any other theory.
(emphasis mine)
BINGO!!