It doesn't matter where the door was, it doesn't matter if they could have walked away - I mean anyone can walk away from a conflict but that also doesn't mean someone won't follow you and attack you from behind. It doesn't matter they were not backed into a corner.
What matters is that they legally have the right to defend themselves if they believe they are endangered. And there is no way to prove that they didn't believe that. This is the way the law works. It's why the law is frustrating because pragmatically everything you said is right. They could have been bigger people, they could have walked and the almost certainly knew they could f--k those guys up - but at the essence of many laws is equality of application irrespective of details such as "could have walked, could have xxxxx". If laws were written to take into account every nuance and variables in a situation they could never be enforceable.
So again, I've said this many times - if you initiate something the law is NOT on your side.
And in this case there is not a lot of doubt who initiated this conflict. "Get the f--k outta here", "What you got?" and shoving someone aggressively is cause for someone to fear for their safety. End of story.
The only way these guys end up in trouble is if a judge deems that the initial force used was enough to stop the conflict and then they continued on and turned the encounter from self defense to assault in itself. That moment is pretty clear - it's when the guy is in the choke hold on the floor. At this point it probably was over - but the problem I was told that the plaintiff/DA will have is that despite being f----d, he tried to aggressively keep hitting the guy. Now again, we all know that that attempt was laughable and not doing anything but it shows that the threat posed was still there so there may be cause by the defense to say "my client still felt endangered and that if he let go the plaintiff would have tried to continue what he started".
You can be disgusted with the fight, feel that the MMA kids went overboard and you aren't wrong but are the "f-ed", yeah not so sure about that.