Realism doesn't need to align with what would be realistic in the real world. On the other hand I firmly believe that every role-player should strive to adhere to any given setting's rules where realism is concerned. We know that people in Eorzea aren't immortal and immune to harm so it's pretty silly when a character charges into battle, cuts down hundreds of pirates in rapid succession and then doesn't even have a scratch in the aftermath.
On the other hand fantasy elements do exist and so if a character conjures up a fireball then it shouldn't be brushed off as silly if it's done in a tasteful manner. Ultimately it all boils down to a mixture of balance, common sense and abiding by the game's established lore. If someone can't do that then they shouldn't be surprised if they're called out on it or avoided.
On the other hand fantasy elements do exist and so if a character conjures up a fireball then it shouldn't be brushed off as silly if it's done in a tasteful manner. Ultimately it all boils down to a mixture of balance, common sense and abiding by the game's established lore. If someone can't do that then they shouldn't be surprised if they're called out on it or avoided.