Yeah, but nevertheless, keeping your personal name as regnal name still is the most consequential thing to do. I am aware that, for example, George VI was called Albert or Queen Victoria's first name was Alexandrina. But when those people were christened, nobody expected them to reign in the future. Victoria only became queen because there were no male heirs left, and Bertie ascended to the throne after his elder brother's more or less unexpected resignation.
My point is, that, when someone is christined as a future king, and Charles certainly was, then it's only reasonable to give them a first name that's suitable as a regnal name, even if personal names and regnal names are not the same thing. George V has done this with his eldest son, the heir apparent Edward, who became Edward VIII, and George VI has done it with his daughter Elizabeth, who became Elizabeth II.
So that's why I found it odd that Charles' parents, being aware he'd be king someday, gave him a first name with a rather unfortunate history.