The MrBeast As are rated on their ability to learn - which is surprisingly a characteristic that’s not mentioned in the Welch model.
MrBeast Bs are As who haven’t got there yet - Welch Bs are not expected to get there.
MrBeast Cs are reasonably capable but are missing out on that crucial learning instinct - again, not mentioned by Welch, who has Cs who are incompetent procrastinators.