"My intuition tells me that cavemen probably had worse quality of life (experience-wise) than modern humans."

That's a very suggestive judgment. It's likely they felt incredibly more in line with their body, emotions and environment. They were probably experiencing states of "flow" for the majority of their active hours, and frequent genuine happiness and sadness. But then it's impossible to measure things like fulfillment and happiness from bone remnants and fragments of DNA, so we wouldn't know for sure.