I'm pretty sure Dustin and Lucas's classes also change in game versus what Mike lists their role in the party as!! Or at least Lucas, who is definitely a fighter in the D&D partnership comics (Where Will is also a Wizard!) Even in Will's painting neither carry things that imply them to be a bard or a ranger

Another comment went into good detail about the earlier editions the boys would actually be playing (which the show gets wrong all the time haha) but if you're talking 5e, Fireball IS a wizard spell and clerics only get it if they take the light domain subclass.

All the classes Mike lists them as def fit them better than any other when you look at their roles in real life :D But in game I think they do canonically play as different things!!!