Truth be told, I've never run a Sword & Sorcery campaign, in any game system, without at least 1 PC as a magic-user.
I think that even though the ("purist Conanesque") fiction doesn't have magic-users as protagonists, RPGs are a different medium and it's okay to have PC casters, as long as you remove the "superhero" spells (fireball, fly, etc).
Wizards incinerating enemies does happen in S&S, but for S&S Fireball should probably be limited to a Near-size blast emanating from the Wizard, not Far range.