At market equilibrium, the expected benefit (revenue) from Bitcoin and other PoW mining would be roughly equal to the expected cost (including electric power cost).

A downside to proof-of-stake systems is that it is a "rich get richer" system: Only people who already have a lot of the currency have a decent chance of getting a block reward of more currency.  PoW is more egalitarian: Anyone can buy a mining rig, and they don't need to compete proportional to the currency holdings of whales but only proportional to their investment in mining (hardware + electricity).