That's efficient if you define efficiency as hashes computed per watt. That's the metric by which less-efficient miners are driven out.

However, this does nothing for the overall energy efficiency of Bitcoin, which could be defined as transactions processed per gigawatt. If energy gets cheaper, that number only gets smaller.

The problem is that there is, by definition, economic incentive to spend an amount of electric energy equal to the economic value of transaction confirmation to all protocol participants.

If someone has money and power already, they can take a better chance to get more bitcoin. How about the other guys and the other guys ... 10/20 years later?