Oh glob, he could have killed 27 instead of 26 people!!! The good guy with a gun came late to the party.Most mass shooters are only stopped by a gun--whether at the hands of the police, or at their own hands when the authorities are closing in. This guy was still armed--he very well might have been going to shoot someone else. (It appears his primary target wasn't at church that day--he might have been going to her house.) Thus engaging him was a good thing to do. This guy was a hero.
The problem I have with the hero narrative is that this atrocity was preventable, however, was allowed thanks to the NRA lobbying that allows guns like these to exist and magazines of 30 bullets to exist. The hero narrative is to try and spin some kind of wonder out of what was yet another mass killing that didn't have to happen.
The magazine capacity is irrelevant unless there is active resistance--and there was none.
The hero intervened, nobody got hurt but the bad guy. That's a lot better outcome than even one more death.