Sure, but "we view casting horoscopes as important"!="therefore we are better navigators." If they value celestial navigation, they presumably study the stars for that reason, regardless of how much emphasis they place on your birth sign. Furthermore, steering by the stars at sea is actually a lot less important for the coastal navigation that was 90% of what people did in those days (you don't want to sail across open ocean any more than necessary; you'd much rather be close enough to the coast to be able to land if something goes wrong). It was huge for e.g. Polynesians crossing the Pacific from atoll to atoll (who were experts on celestial navigation, although I'm not sure what if anything they did in the way of astrology); it was fairly irrelevant for sailing around the Mediterranean (where, again, you'd mostly hug the coast).
Besides, seabound just lets you navigate rivers, where celestial navigation is even less important.