I would say that for standard shotgun, that's pretty good.
8 to 9 rounds is reasonable. Yeah, you could to the trick double tube guns for more but then I would say, get a carbine.
Tom Givens had the concept of time in the fight. That means how long you can stay fighting before gun equipment issues take you out. Thus, the less capacity the quicker you are out of it. For a shotgun, with 5 - you are out pretty quick. Unless you are the person who hits every target with a stopper, you are out quick.
As I said, reloading under stress is fun. Givens had us do a drill with 4 people in a row. The first guy loaded one round and shot, the guy next to him had to load as he shot and so on down the line. As it reached the end of the line, the first guy had to load two and fire, the next guy loaded two as he fired, then three and four - by the time we got to four - it was tight and screwing up the load and rack was a real possibility.
Also, in another class - moving through a 'shoot house', why surprise - you could miss a real close target. Now how could that happen.
One hoot for double barrel fans at the NTI - you start in a smock which was to simulate being naked. You pick up a coach gun and a box of shell and a flashlight. You have to navigate your house with multiple bad guns - shoot, reload, light and hold on to everything. Remember you are naked, so to speak. It was fun. Shoot the gun, reload , forget that the safety came back on.
After shooting two targets, here's a surprise one popping out - so no rounds in the gun - it was close, so I butt stroked it. OK - having a carbine with 30 would be a better plan - in my mind.
Now, I wouldn't feel helpless with my Defender and 8 rounds but going for less, when more are possible - I just don't see it.