One of the biggest points of the article was that Mercury has abundant available energy from the sun - just stick up some solar panels, or the thermal gradients are perfect for running turbines - large enough to supply a lot of power, but not so large that engineering becomes hard. While there are some energy sources available underwater, it would seem to be much more difficult to exploit them.

Yeah I think so. It wasn't comparing to Mercury though, just pointing out underwater probably isn't an oasis.