Lots of issues here, bro, and enough complicated branching to probably make it better suited to a thread discussion elsewhere on GlockTalk. Best I can do in the short answer forum of GATE is:
1: Some would suggest that cold cocking your antagonistic drunk buddy would have been the quickest, most all-encompassing solution.
2: Classic example of my friend John Farnam's advice, which reads in part: "Don't go stupid places with stupid people." If this guy is gonna get smashed and start fights in bars full of dangerous people, and you absolutely HAVE to babysit him when he's drinking, best bet is to rent some DVDs and buy some pizza to go with the booze, and do it at home where he won't get you both into (as much) trouble.
3: Size and strength is an element that gives you disparity of force. So is the physical prowess you mentioned, but you didn't go into detail on your hand to hand background or just how decisively you put that first guy horizontal.
4: Force of numbers of course gives the others an element of disparity of force; no matter how big the moose, a large enough wolf pack can take him down.
5: Judge and jury would be looking at whether you attempted to de-escalate or remove your buddy between when he became antagonistic and when the crowd became assaultive. Absence of any attempt by you to quiet him down or get him out of there would make you look like part of the problem, not part of the solution.
6: Drawing a gun might indeed back off a mob. You'll want to be double checking on the legality of carrying in a bar in Montana, though. There's also the possibility that someone in the crowd might have had enough "beer muscles" to jump you for the gun...or pull one of his own.
I hope you've had a long talk with your buddy once he sobered up, and maybe discussed changing the recreational drinking paradigm.