Theorists believe that string theory is self-sufficient. But in my opinion, it should be crossed with ether theory. This hybrid will be successful.

It would be useful to learn the basics about it, e.g. from here: https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://cds.cern.ch/record/204950/files/slac-pub-5149.pdf&ved=2ahUKEwjgxf6FquSNAxXAUaQEHR-MOYo4ChAWegQIKhAB&usg=AOvVaw1c0tnHIBfDubovR_nQLZU5

before the relevance of D-branes was recognized and here: https://arxiv.org/abs/2311.18456 for understanding the relevance of D-branes.

Which implies that string theory requires not only taking into account one-dimensional excitations, but excitations, also, with more than one spatial extension, for consistency.

String theory is the mathematically consistent description of relativistic extended objects, nothing more and nothing less. So that's one reason to be interested in the subject.

Another reason why anyone who works in physics would be interested in string theory is because the excitations described by string theory have the properties necessary for explaining the statistical mechanics of the microstates of black hole spacetimes, that can resolve the expected thermodynamic properties of black holes, when these are probed by quantum matter, cf. https://indico.cern.ch/event/58217/contributions/2047275/attachments/991938/1410514/sen.pdf.pdf and

https://indico.ictp.it/event/a11155/session/33/contribution/26/material/0/0.pdf

for a review.

So while the quantum properties of strings and branes are, still, not fully understood, what is understood turns out to be sufficient to grasp how the thermodynamics of black holes can be consistently described, when the matter that probes the black hole spacetime displays known quantum properties.

String theory does provide a quantitative description of hadronic resonances-that's how its relevance was discovered in the first place. Supersymmetry didn't play any role in that context. What is not known, in fact, is how the low energy behavior of hadronic resonances, as described by the so-called dual models, aka string theory, matches with what is known about QCD at high energies. That is a challenge for lattice QCD.

The microstates of black holes become resolved when quantum fluctuations of spacetime are relevant. That is the context where supersymmetry becomes relevant, because it is only for extremal black holes that the matching between the microstate counting and the thermodynamics can be done in a controlled way. This doesn't have anything to do with what the LHC can measure, so it doesn't make sense mentioning it. The emphasis is on doing controlled calculations, not setting up real experiments. What could be the appropriate experiments is, still, not known-but what is known is that black hole microstates don't have anything to do with physics relevant for LHC energies.

It's also known that supersymmetry, insofar as it is relevant for particle physics, must be broken, since were it intact, it would imply, among other particles, the existence of a particle with the same mass and charge as the electron, but with spin 0. Such a particle hasn't been observed. How supersymmetry can be broken, however, isn't completely known, so how to search for the putative superpartner of the electron and of the other known particles is, also, not known. What the LHC can and does rule out is the hypotheses about how supersymmetry might be broken.

However the supersymmetry relevant for particle physics doesn't have anything to do with the supersymmetry relevant for string theory; how to relate the Standard Model to the way string theory describes black hole microstates isn't known.