There is certainly a lot of pseudoscience used in badly applied UX and also there is also a lot of science involved in its application. But UX itself is neither science no pseudoscience in my opinion. I can confidently say that in the 15 years I’ve been using research to inform design, that I haven’t ever proven anything with UX research. With product experiments (A/B tests) on the other hand we’ve proven things of a very very narrow scope. These proofs give us confidence about other decisions we take, but they don’t prove those decisions to be the right ones, they are just more likely to be good as a result.
UX research is more about opportunity and risk than it is about proof. The product improvement idea you had never thought about until you started observing users. UX research gave you that. Or the confidence you got from finding and fixing all the bits of that design which didn’t make sense to people. Nothing there is about proof or validation, it’s more about having confidence.