I found a legendary monowire before I even finished Act 1 just from exploring and side missions and gigs. Your experience doesn't match mine.

To be fair, you can grind a bunch in Act 1 Watson but you can't leave the vicinity of the district. The bridges and exits are blocked off GTA3 style and if you try to head to the badlands the game literally flashes a warning and tells you to turn around before just plopping you back in the city