What you are witnessing with that video is what surprise does to even the best people. Note that the perp didn't make it much past where he ran off camera, he was tackled and detained.

I think all of you have an unrealistic expectation of how effective even a trained person can be in engaging a threat that appears by surprise, and is rapidly moving.

What concerns me is the institutional incompetence that is shown in that video. Why was the bathroom that man went into still open? Where were the cordons to direct the flow of people? I get that they were breaking down the access point, but it is still an access point. It should not have been possible to rush it like that.