When it comes to playing, the bassist ultimately decides the pace that is played at. As to what is actually played, it is not set in stone who is in charge. The bassist can present some of their ideas and the guitarist can input some of theirs. Like playing with guitarists, it is a mutual exchange of ideas for the most part. When playing bass, it is usually fairly easy to find someone who wants to play, because most guitarists don't get many opportunities to play with bassists.
Bassists have all the real opportunities when it comes to getting in something like a band.
After all, a drummer would take a lot of pressure to keep time off of Jesse. It would sound pretty damn cool to have a drummer too. We might even start a band. Unfortunately, there is not a drummer in the whole place. Or a drum set, for that matter.