I think that's the case today - rather than think up an original or classic name, people take one that's fashionable - like McKenzie for a girl - and fiddle with the spelling so it comes out Macenzee or something. But centuries ago people first of all weren't literate mostly and secondly lived in amazingly small communities. The local priest would write the chosen name down, and his education was sometimes unreliable so the spelling could be odd, and he'd also often use the Latin form like Philippus when the parents would only ever call the child Philip or Phil or Pip. So there were very few names in circulation, and the written forms didn't always match the spoken ones. You can see that after a couple of centuries there could be a lot of variation within the same language.