The "threat" has changed in my view, and more gun is never a bad thing.
"We", as a group, appear to like to argue a lot. More gun is never a bad thing until it reaches the point that you have so much gun you leave it at home. There is something distinctive to the contours of a revolver that, for some people, make it easier to carry than small autos that are dimensionally very similar. I expect that many people, myself included at times, carry a revolver because we are not going to carry something else.
We seem to be arguing different sides of the same coin in a lot of these discussions. The OP is not wrong. Most of the time a civilian would need a gun for legitimate self defense five rounds is going to be enough - the numbers on this are all over and the samples are not all the same but the average and median rounds used in a positive outcome use of force seems to be around 2 or 3 (I found several that come up with 2.X which would favor 3 but were technically closer to 2). Its interesting to note many of these only reference positive outcomes. Did those without a positive outcome fail because of lack of rounds fired? Skill of the defender? Skill or number of the aggressors? There are a lot of confounding variables that are not something one can isolate.
BUT the other argument is not without its merits either. If you run out of ammunition its going to be a MAJOR problem and regardless of the actual numbers of shots fired you are much more likely to run out of ammunition at 5 rounds than 10 (or 15, or whatever).
And you know what. Both those above premises can exist and be weighed differently by people making their own choices for what effective self defense means for them.
In the end though it seems very few people are advocating a G19, two spare magazines, and a G26 as back-up for a total of 57 rounds by my count. Even fewer are advocating for a long gun though the vast majority of us seem to argue, if we are ever going to be in a gun fight, want to have a long gun and a bunch of friends with us.
We all make our choices, we live with the result (or don't), and hope we never have to test it. In the end we are all mortal and its just a matter of how mortality finds u. I'm not certain why we, and yes that is the inclusive we, feel the need to convince each other that the decision we have made for ourselves is the right one for others.