Ralph Carr wrote in 1865 that he thought maybe the "Maes-" element was a pre-Viking one in Orkney. But he also thought the locals were speaking a Gaelic language - so he dismissed his pre-Viking idea because he thought there should be "maes-" all over the other places where Gaelic names are common. Of course, they aren't. And of course, it's now thought by almost everybody that the ?Pictish language is far more related to the Brittonic (Breton/Welsh etc) languages than the Gaelic ones. Or in other words - what had been his main objection to a pre-Norse origin no longer applies.

Mount Maesry, I think, fits the Celtic "maes-" as well. OK, so it's right next to the sea - but isn't it enclosed by the sea, and reasonably flat and grassy? Isn't the location almost like a field, with the sea instead of fences?