A "method" in general gives you a variety of exercises, tools, tidbits in order to get around and learn the notes of your instrument, scales, fingerings, etc. Maybe including some basic theory. A theory book usually assumes you know the basics and are ready to learn about chords, keys, how they interact, and how to construct bass lines from knowledge rather that simply putting your fingers where the tab tells you to.
IMO, and I get a lot of flack for this here, but I contend that a good, versatile bassist is often the band member who knows the most theory. There are other approaches though, but in my view they may limit the genres you can play.
IMO, and I get a lot of flack for this here, but I contend that a good, versatile bassist is often the band member who knows the most theory. There are other approaches though, but in my view they may limit the genres you can play.