True leaders don't just declare themselves as such. There are many talents and skills that one must have. They must first and foremost have the trust of those under them and show judgement in difficult situations in order to gain that trust. Experience and common sense are also good to have.
These attributes are universal from a small band of survivors to that of a national leader. On the topic of a Class 4 outbreak, governments will be little more than groups in exile. With a breakdown of society, there might be some who attempt to declare themselves 'leader' by force perhaps. But not everyone is going to blindly follow that person or group. Someone who simply says "follow me" may soon see those who would be his followers fragment into other factions and those that were once on the same team may find themselves fighting one another.
Agreed. A leader will not look to lead. They might even avoid it. They look to survive and by surviving they are an example to others. They tend to get a following and the next thing they know they are leading. Run like hell from someone who wants to lead.
Not really. They can survive but many are there because of mental illness and disorders. Short term they could be very helpful. Many would have another break and head for the hills again.