Skinner's theory is no longer relevant because more predictive theories of animal learning have come along. Similarly, Newtonian theory is no longer relevant but that doesn't mean it now fails to predict.
But that doesn't mean it's not longer relevant. Suppose you want to model a fluid mechanics problem where the speeds are all well below the speed of light (so any fluids problem outside of a few astrophysics scenarios). You will be able to get far further using Newtonian mechanics, and derive far more results, because of the relative simplicity of Newtonian mechanics. Trying to derive everything using special relativity would get very messy, and would impede your understanding of what matters at slow speeds.