That's funny because I was actually talking about your field! (whose math is borrowed from one of the subfields of physics) I haven't so far met even a single c

That's funny because I was actually talking about your field! (whose math is borrowed from one of the subfields of physics) I haven't so far met even a single chemist or material scientist who actually knows what they're running, even when they have access to the millons of lines of code they're using. And I don't blame them (or call them "mediocre" as you do), because they only have 24 hours in a day and only one life! I met only one computational physicist so far doing DFT who used to write his own code back in 70s, but he admits he has no idea what VASP and others are doing nowadays. If you're claiming that you actually know how VASP or Quantum Espresso (or any other similar significant piece of software) works in depth and you can tweak/replace any part as you like (which I'd find very very hard to believe, millions of work hours go into the development of those), you'd nevertheless be the exception in chemistry not the norm. The most common high-level tools theoretical physicists like me use (such as Mathematica) don't give access to source code, on the other hand, so we can't make Mathematica not use MKL and not suck on AMD.