I can only speak for the Mylchreests where my Ballaharra lineage is proved back to William McYlchreest of Kerrowgarrow, German, died 1644. Earlier there were McGilchrists living on the German Abbeylands (e.g. in 1540) who are probably the same line but presently unproven. In 1513 there are a few McGilchrists and an Ine Gilchrist in Lezayre.

For the date when the Manx Mac Names became hereditary, see Prof. R.L. Thomson's article in the Proc.I.O.M.N.H. & A.S.
It all has to do with when the forenames were current. For example in 1511/1513 many men were called by English or Norman names like John, Thomas, Robert, William, Edmund as well as Gaelic ones like Finlo, Donald, Mold &c
If the patronymical names had formed that late we would be like Wales with a preponderance of surnames formed on John William Robert Thomas i.e. Kewin, Quilliam Crebbin & Camaish instead of the enormous spread of names incorporating pure Gaelic or Norse forenames which were well out of use by 1511. These include names such as Cathain > Cain: Cannanain> Cannon: Caisin> Cashen:Luathod> Clague: Anghois> Creer: Sveinn> Quine: all the Thor names & so on.
This is all fascinating. It would be good to plot the distribution of the surnames in 1511/1513/1540 to see if there were particular areas where the names stemming from Gaelic, Norse and Norman names were clustered. You could look at the McGil names too, but I think they are just as "Manx" as the others formed on Gaelic stems.
Obviously there are lots of Manx names formed on the Gaelic fornames which were still popular in 1511 - Kinley, Cannell, Cubbon + you could see if they had a different distribution. Just as a taste in Baldwin almost all the name were formed on obsolete Gaelic names - Quine, Kelly, Cowin, Lewin, Creer, Cannon altho' there were exceptions.