I can survive Hazard lvl. 4 solo with my trusty buddy Bosco. The Dreadnaughts are challenging though! But on the whole whether you do or don't play online this game is a blast!
*Edit: You'll probably not be able to do the Deep Dives though as they are primarily group content.
Just want to clarify that deep dives, like all our other missions scale their difficulty based on the number of players.