I am trying to be careful with the word “theory.” My understanding is that a scientific theory is not just a random guess. It is an organized explanatory framework based on evidence, observation, testing, predictions, and reasoning. Evolution and germ theory are strongly supported. String theory may be a useful theoretical framework, but should not be treated as settled proof in the same way.
Here’s support for you position from Stephen Jay Gould:
Facts and theories are different things, not rungs in a hierarchy of increasing certainty. Facts are the world’s data. Theories are structures of ideas that explain and interpret facts. Facts do not go away while scientists debate rival theories for explaining them.
He also wrote:
In science, “fact” can only mean "confirmed to such a degree that it would be perverse to withhold provisional assent.
Unfortunately there are quite a lot of terms in science that are misleading. From planetary nebula to the big bang. From quantum leap to the god particle. And indeed “theory of everything”.
“Theory” has to be up there as one of the worst offenders at this point.
Because, firstly you have the popular misconception that theory just means “guess”. As you hear in, for example, “Evolution is just a theory!”
And most scientists, and reference material, will push back and say that a theory is actually the highest level of verified model, hence we have the theory of gravity, atomic theory, germ theory etc.
But then secondly comes the question of why string theory is a theory, when it hasn’t yet been verified? And this is because in some fields like physics it means something more like a formal system of model(s) that, in principle, can be used to make accurate predictions.
I think it’s because in fields like theoretical physics, an awful lot of work and development of a model can happen before it gets to experimental confirmation. And, in the meantime, what do you call it when such a model is impressively producing known data like particle masses?
So it’s understandable why the word “theory” might be used in the second case too, but it does result in a lot of confusion when using this word.