Question

was humanity better off because it had fire and civilization or worse off because the cost was misery and disease

Answer 1

They were better off. Without the discovery of the uses of fire, mankind would not be here. Fire led to the rapid increase of newer, more advanced tech, such as a sword instead of a club.

Answer 2

it was better because it could survive and reproduce and evolve quicker with its mind growing bigger and getting smarter every day.