[rb12345]

While it's true that your remaining miners get more coins, kWh/coin is far higher and the power costs are most likely in normal currencies. In addition, the transaction times would become highly variable, reducing the utility (and hence value) of the cryptocurrency. Given both those points, you could cause huge instabilities in hash rate assuming you could persuade enough miners to join in.

The important point is that an attacker could use this just to wreck the cryptocurrency in question, although they may simply buy more coins at the lower price and profit from any rebound.