Obviously, nothing in baseball is 100% predictable. That is not the same as saying that there are no repeatable skills in baseball. There are several hitting stats that correlate strongly from one year to the next.
The ability to make contact is a strong repeatable skill. Other offensive skills that are repeatable are K%, BB%, GB%, ISO, SLG, OPS, OBP, and wOBA, based on their year to year correlations.
Some things that do not correlate well, meaning that a lot is left to randomness or luck are BA, BABIP, LD%, and Clutch.