There is a difference, between playing as a mage and there being “mage gameplay” in a game. It’s similar and perhaps easier to illustrate with thieves/rogues. Almost every rpg lets you play as a thief. But few actually have any gameplay built around “thiefy” activities. You don’t generally sneak around buildings at night, case out targets or bribe guards. The gameplay is almost always focused around combat. In other words : “fighter gameplay". Playing a thief or a wizard is pretty much playing much like playing a warrior, but with different tools to kill enemies with.