Sooner -
I used to live in Scotland.
While it is accurate to say that Mac/Mc can't be attributed exclusively to Scotland/Ireland, it is an exaggeration to call it "complete and under nonsense ".
Yes, both prefixes have historical origins in each place, but Mac was significantly more prevelant in Scotland. Movements over the past two centuries have diluted that fact, but even today it is still true.
When people would call and say "this is Ronald McDonald" I would say, "can you spell that?" and they would say "the Irish McDonald". In is commonly accepted (even if inaccurate) to refer to each spelling as either the Irish spelling or the Scottish spelling.
Anyway, thank you for pointing that out, as you are accurate, but I think the reality is a bit more nuanced than than bright line drawn in the link you posted.
Back to McGuffie - dude was the only thing Michigan had going for them. Take him away, and Notre Dame pounds them 38-0.