Some days the shotgun is only a bb gun; some days it is a bazooka; some days the same group of divers will each have a different velocity to negotiate.
It was easy for you, when you went through.
I position myself next to the shotgun (left in the picture) and if you had not followed my example for
safe exiting procedures I would have stopped you and made you follow instructions. Sure, you made it, but what if the next person, with less skill than you had a more powerful surge to deal with; your example of not following instructions could have caused another diver to be injured.
There are only a couple small pieces of black coral inside the Cathedral, and no coral of any kind anywhere near the shotgun.