I believe we were able to survive in ancient times by becoming visionaries, shamans, or any other sort of spirit talker.
Our delusions made the legends and myths we hear today.
We made predictions and we were either right or wrong and depending on that the community either shunned us for scaring them or praised us for coincidentally recognizing patterns in the world and making predictions that would then become true.
Imagine yourself unmedicated in the times of tribes.
You have a delusion of a tiger coming to attack, you put the tribe on high alert.
Thankfully a tiger comes close vicinity of the nesting grounds.
You are praised for seeing the threat beforehand and now we have a dead tiger and meat for a week.
I think most of us were useless and sent off into the woods to starve alone if we weren’t killed outright. Odds are that the “shaman” of olden days were highly functional con men like the megachurch preachers of today.
Treatment for SZs has historically been quite barbaric. It was legal to sterilize us and physically scramble our brains using tools pounded up our noses in the last half century. What makes you think we would have been treated better in older times when we had zero legal protections at all and life was even cheaper? They would hang a six year old for stealing a loaf of bread in England a few centuries back.