“your basic instinct is to hit the deck and escape”
Absolutely! Shock and awe is designed to catch the victims ( enemy ) off guard and it takes some time for most to process unexpected information. The passengers on Flight 93 took some time to steel their resolve. The entire episode in the theater only took seconds and was over in a minute or two. The shooter positioned himself so as to limit the approaches available to attackers and wore armor in case someone shot back.
I wouldn’t have any criticism for the victims in this sad case.
This is not to disparage what they did. They were heroes. They were trying to get control of the plane to save themselves from certain death.
For those who live in a fantasy world and have these Walter Mitty moments thinking how heoric they would have been, it is a bit nauseating. I have experienced a real life situation of being captured by armed intruders. Self-preservation is a very powerful instinct.