We all know, I think, that styles make fights and there are plenty of examples of ATG fighters losing or struggling with distinctly lesser fighters than themselves due to problems with a particular style. To name just two examples: Sugar Ray Robinson lost to Randolph Turpin and was given all he could handle in their rematch; Alexis Arguello lost to Vilomar Fernandez. In most of the fantasy matchups on here, the ATG never loses to lesser fighters. So try and think of an ATG who he either loses to, or at least seriously struggles with a non-ATG.
I’ve always thought Johnny Famechon ( maybe not an ATG but a beautiful boxer) would have given one of my personal favourites in Alexis Arguello (a text book ATG) fits with his style. That defence, movement, speed and strict adherence to his game plan could’ve caused Alexis big trouble given Alexis tended to excel against guys who lingered in his wheelhouse which Fammo would absolutely not have done.
Charles losing to Overlin was a stylist thing IMO. Charles' big weakness at MW was that he was wasn't filled out properly, which led to a lack of power, sun-par conditioning and him being a bit of string bean. Overlin, a consummate swarmer, took advantage of this when he well... you guessed it, swarmed! The draw in the rematch also seems to be a bad decision (in Charles' favour). Although Overlin is a great MW, it's not someone who you'd expect Charles to lose to. Turnero did something similar but I'm pretty sure this is considered a robbery.