We don't know the mechanisms of plenty of things that we accept as proven with scientific principles, like most of pharmacy.
And what about physics before Newton? Or before Einstein? In fact, we still don't know exactly how gravity works. Or magnetism. At what point are you drawing the line of being able to "elaborate the exact mechanism"?
You never elaborate the exact mechanism. But if you can consistently make accurate predictions, you're onto something.
The real argument is about the validity of the predictions. Core science - basically undergrad - is very good at making predictions in its domains of interest. Outside of that everything gets more speculative.
The real problem with soft science research is that it cargo cults data -> statistics into data -> weak correlations -> "truth." And that's not how good science works - because there's just a statement based on correlations that may be accidental, and there's no attempt to make a model at all.
And what about physics before Newton? Or before Einstein? In fact, we still don't know exactly how gravity works. Or magnetism. At what point are you drawing the line of being able to "elaborate the exact mechanism"?