Haha I was thinking the same thing. But then I realized that these are all sites dedicated to the Archangel Michael, each built centuries apart from each other, thus with no obvious means of coordination.
As to the issue of this not really being a straight line since this is only a straight line on a Mercator projection, I don't have a globe so I can't be sure but to me it seems even on a sphere this might be a line, although an arc at any rate, still a continuous line from the first to the last. It wouldn't be a serpentine pattern in other words.
Even if the line on a globe isn't perfectly straight though, it's still amazing that on a Mercator projection it is a straight line. So there's that.
It would be an unusual, goal-seeking arc through a set of cherry-picked data points. I would not assign it much significance.
It isn’t. Google Maps draws great circle lines. If you draw a line from Skellig Michael to Mt Carmel, you’ll find that the other sites aren’t on the line.