The issue with string theory isn't an inability to explain what standard QM can explain, it's the problem that so many formulations of it may not be falsifiable

The issue with string theory isn't an inability to explain what standard QM can explain, it's the problem that so many formulations of it may not be falsifiable. Making predictions along aside another falsifiable, real theory, without offering falsifiable predictions yourself... that's where String theory finds itself for the most part. There are still some formulations that haven't been ruled out by observations such as LHC data, but not many, and they're not necessarily the ones that were anyone's darlings.