Shield master doesn’t work against fireballs, it only works against single-target spells.
As for tieflings… well, a wizard with the elemental adept feat can just ignore fire resistance (and ensures that the minimum damage on the fireball is bumped to 16). Or a Scribes wizard can just have Spirit Shroud in their spellbook, cast necroball, and be done with it. Or a sorcerer with transmuted spell can use another elemental type too, though for them it costs SPs.