I think you are maybe making too much distinction between MacSween and MacQueen. You seem to view "MacSween" as the older, or original spelling, and "MacQueen" as a modern Anglicized form.

In truth, both "MacQueen" and "MacSween" are Anglicized names. The Gaelic is Mac Shuibhne. (And even the Gaelic spelling will be different depending upon the era). So far as I am aware they are both considered perfectly acceptible ways to Anglicize the Gaelic name.