I think I would agree with you for the most part, especially calmness under pressure. Specialized knowledge, or even just basic knowledge (how to stay warm, how to build a fire, etc) is helpful, but I have had good trips with many people who did not know how to set up a Z system (we use it for vertical evacuations).

I guess I am a little unclear about "mental toughness." It really helps if one can stay focused on priorities and blot out secondary issues. If one has prior experience (previous unplanned nights out, actual first aid situations, etc) it is a big help. The first time is always more of an adventure.

In an emergency, it seems to me that what counts is not just individual expertise, but the ability of the group to come together and cooperate, work productively, and get the job done. Sometimes when it hits the fan, the group, as such, disintegrates, and first responders will encounter absolute chaos. Other times, the group operates effectively, frequently without a designated "leader", and stabilizes the situation quite well.

I like groups where I know my experienced companions capabilities, perhaps with some new folks added in. They may have unexpected and welcome skills. Those groups generally work out well.