Generally tribes have arranged marriage systems and will trade daughters with different tribes so that the boys in a tribe have someone to marry and it prevents inbreeding from a tribe just fucking their own people for generations, so I would guess that inceldom is virtually nonexistent in such primitive tribes. Also there is a lot of reason not to let incels become a thing in a small tribe, because you don't want unmotivated and envious tribal dudes putting a spear in another dude in the night because he's the only one not getting pussy.
Yes it is true that many chiefs will have multiple wives and access to more women than his lessers, but that doesn't mean that any tribe works where the chief just gets all the pussy and lets the men all rot alone; that would just lead to mutiny and him being overthrown.