This is what I’ve read.
A little bit of negative camber in the rear will give little bit more grip while cornering and high speed stability but only up to a point. Excessive negative camber will cause less grip like you said.
There is more grip with a little neg camber because when cornering, the tire rolls a bit. The rear neg camber will keep the tire from rolling onto its sidewall and give the greatest contact patch possible.
Drift cars and crap run crazy amounts of camber so that the rear can slide out easier.
Anyone feel free to go more in depth or correct me if I’m wrong.