Regarding the wellness of Primitive versus Civilized Man, the relevant passage in Lucretius is V:988-1010. He contrasts the two using three specific examples. To summarize:
1. Primitive humans were on balance more likely to die by predation or festering wounds. Civilized humans are seldom devoured by beasts, but often die in droves at sea or on the battlefield.
2. Primitive humans suffered from a lack of food. Civilized humans, from overabundance ("penuria" vs "copia"). What the disease is that results from rerum copia is not specified; gout has long been thought of as a 'rich man's disease'.
3. Primitive humans unwittingly poisoned themselves. Civilized humans kill themselves [and, it is implied, each other] with deliberate skill.
There's no question that civilized humans today are much healthier than their primitive ancestors. But for a 1st century Roman the arithmetic was quite different. There's an amusing story in Caesar's De Bello Gallico about a Gallic chief who forbade the import of goods, especially wine, from Rome. He didn't want his hardy frontier tribe to succumb to the ills of Roman culture and civilization.