Earlier quoted context omitted.
> Quantisation is a nearly well understood process The layman’s explanation I received for this, perhaps incorrectly, is that you fill in variables for factors that you don’t understand or can’t measure with whatever value makes the rest of the theory / equation work. Is that at all correct?
No, that sounds more like a (very distorted) description of regularization and/or renormalization. Regularization techniques take effective field theories like the Standard Model, which are known to be inaccurate at high enough energies, and isolate their low-energy behavior. For example: classical electrodynamics, interpreted naively, says that the total energy stored in an electron's electric field is infinite, sin…
Notably, in a less rigorous field, this process would be called "doing science to determine physical properties of things", which most people consider an acceptable pastime for physicists. As it turns out we can be pretty confident that the "experimental evidence" is bunk and there's something going on the theory can't account for, but it's funny that so many of the Monday morning quantum physicists think all this math stuff is just confusing the issue and pure, blind empiricism is the way to go.