After running this mission four times, I must say soloing is much easier than going in a group. Not only do those Oilers die in two hits (or 4 with Poison) while in a group they survive long enough to deal a massive amount of damage. The only time I ever had trouble was on the final arena and that was because I got trapped in a corner with my shield broken. Even Gran Faust on the Oiler-Barons take about 10 hits versus 50-ish hits.
So, yeah. Stuff. GET SOLOING YOU PEOPLE.
I guess you start solo when you finish the level. That's why it easy.