'Guess Sort Name' has historically had a very bad reputation. Pre-NGS is would simply copy the artist name and always render it as 'Doe, John'. Post-NGS is pretty much copies the artist name as entered.
I think having the choice of these options, and not trying to guess, is by far the better idea.
Thus, I propose that the Add Artist page has two buttons: Copy Name, and "Last Name First", which render it in the appropriate last name first sort manner such as "Thorton, Billy Bob". This way users can pass pseudonyms straight through, or if it's an actual name, automatically fill it in as appropriate.
The guessing is still left up to the user, but in this case there is likely no better way.