First punch is probably justifiable... second and third punch were perhaps a bit excessive... his manager/the club owners ought to be worried a bit. While perhaps he can still justify it in terms of avoiding criminal charges from the police, the guy was clearly in no state after the first punch and two more punches to the head/dropping him to the tarmac could have done some serious damage - this is where people can get killed and the club might well get sued.
I guess there is the off chance that the guy was trying to restrain the bouncer and had legitimate reason to do so (we don't know what started it all) - though slightly undermined by him throwing a few weak punches at him from the clinch near the beginning.
With regard to the second and third punch he gets up and doesn't seem to try and throw a punch, it isn't clear what his intentions are, possibly he's just wanting to complain/mouth off... not a bright idea but also something that doesn't require a 2nd and 3rd punch to deal with. There is another bloke who gets a punch too in the blue shirt, he doesn't seem to have thrown punches (I might need to watch again) and it isn't clear if he was fighting or trying to break things up... he trips and then turns towards the bouncer, we don't know what he says but he gets a punch and is on the floor with the main guy.. that might not have been too reasonable either.