I doubt that they teach incorrect theories today. A thing to understand here is that all theories are considered correct, the only difference between them being the area which they describe the best (or more efficiently). They are all approximations and thus can be thought of as all being correct and incorrect at the same time. From the philosophical standpoint, however, you are correct - modern theories do replace the older ones; unfortunately, to apply the quantization procedure you need to be able to understand what it is that you are applying this procedure to - and that is something that is described by the old, "incorrect" theory.

I think context/scale/application is important. Classical Newtonian physics takes us pretty far pretty accurately until we get to more micro or macro scales. For example, if wanting to model a physics engine in software and the Newtonian models are considerably more performant, then could make sense to sacrifice the accuracy.