Regarding O'Brien, the timing of the fights may have been part of the reason for the poor 1st period. Team had to come out and penalty kill too much and it can kill the rhythm.
On the other hand, I think he's been kept around because he's basically always willing to start something if the opponent is taking liberties.
I don't necessarily think he needs to be doing this all the time, but if the young guys are going to take anything away from it, perhaps he's done his role and in the future when he's likely not around, they will step up their own physicality and defend each other when it happens, albeit with a more measured response so we wind up with less extraneous penalties.
His puck handling and decision-making with the puck are usually among the lowest on the team, so I can't really see him being able to stick around as the prospects start coming up.