If we're doing a meta discussion on the quality of arguments it ought to be pointed out that Popper is not exactly modern any more so like objectivism, falsifiability is not some kind of holy grail any more.

A bigger issue with string theory is that we don't fully know how to make it describe reality, but it still describes some general principles we can test and learn from and I think it's the most successful quantum theory with gravity so far, even if it's not the right quantum mechanics and the right gravity.

Any property like super symmetry that could in theory be tested would prove parts of it. We lack a way of doing so, especially in a controlled manner, but particles have been identified from a single convenient photograph.

Without detracting from anything you said, all I meant is that a lot of people make the argument of "we can't test it" when it's likely that the "can't" is purely a technological limitation. If those people knew the definition of falsifiability as stated on Wikipedia, they wouldn't make such a stupid argument.