Teeth used to get cleaned by means of chewing harder food regularly, and they needed less cleaning to start with due to a lot less sugar in those foods though

I don't follow the logic. Human teeth would be better if more children died? That "quality check" only applies if an organism dies before mating, which happens usually around teenage years for humans.

Maybe those hunter gatherers had better teeth because of what they ate. There seems to be too many other potential factors to simply pawn it off on Darwinism.

https://www.npr.org/sections/health-shots/2013/02/24/172688806/ancient-chompers-were-healthier-than-ours

In a study published in the latest Nature Genetics, Cooper and his research team looked at calcified plaque on ancient teeth from 34 prehistoric human skeletons. What they found was that as our diets changed over time — shifting from meat, vegetables and nuts to carbohydrates and sugar — so too did the composition of bacteria in our mouths.

However, the researchers found that as prehistoric humans transitioned from hunting and gathering to farming, certain types of disease-causing bacteria that were particularly efficient at using carbohydrates started to win out over other types of "friendly" bacteria in human mouths. The addition of processed flour and sugar during the Industrial Revolution only made matters worse.

Nah.

There seems to be a genetic variation that eliminates some or all wisdom teeth. It arose in Asia so long ago that the people who populated North and South America also had it. And in most populations it is still not very prevalent (less than 50%). Despite having been around for ages.