That is average number spread out over all the terrorists and not median. Trying to merge those two concept is a common way to use statistic to mislead.
The question was if a shotgun wielding guy posting a video on Youtube is more likely to kill more people than a shotgun wielding mass murderer who robs liqueur stores. To clarify, he doesn't have a time machine to suddenly transfer himself to 2001.
Not fair; the public was not prepared to deal with that situation; now they are. Pilots carry; attendants and passengers are knowledgeable to fight back. And that's including revoking most of what the TSA has become.
Do some rough math on 9/11. 9 terrorists and 2977 deaths (331/terrorist).
The most prolific mass murders have "alleged" death tolls in the hundreds, but most are only multiples of ten.