Forget everything you know:
“Mc” isn’t the Irish equivalent to the Scottish “Mac,” nor does the difference denote socioeconomic status.
“Mc” is simply an abbreviation of “Mac.”
Any amateur genealogist has learned to be phonetically tolerant in the search for last names, and the Mac bunch is no exception.
Incidentally, “Mac” is the Gaelic word for “son.”
Hence, MacDonald, or McDonald, is literally “son of Donald”, meaning exactly the same as the last name Donaldson.