Why would you assume the wizard would use this tactic against a creature with a breath weapon or AoE? Even where it isn’t obvious (dragons have breath weapons? You don’t say!), it seems to me that finding things out about your opponent would be a simple Int check, and wizards are really good at those.
If summoning hordes of minions isn’t a good tactic, you change your tactic. And wizards, the kings of versatility, with 14 spells prepared, are very good at that.
Meanwhile, the fighter has a lot less versatility. If his preferred tactic is ineffective against a particular enemy, there isn’t a whole lot he can do.