First level is special in any campaign, because everybody in the party is easily one-shot'ed, not only the Wizard/Sorcerer. At that level, even the discrepancy in attack bonuses isn't consistent enough to make a difference in the face of the mighty d20 with its huge variance. Every party composition must come to grips with the fact that, very likely indeed, one of them will bite the dust at 1st level, before ever reaching the relative safety of 2nd or even 3rd level (where suddenly almost nobody is easily one-shot'ed).
Therefore, I'm of the opinion that at 1st level, most party compositions will work equally badly. 2nd level and higher, a broader spread in ability will be useful (such as 2 frontliners, a utility guy (caster or skillmonkey), a BC guy/buffer, and one of them should be able to heal somewhat).
I believe that from 4th level onwards a pure arcane caster party can be very feasible, maybe even optimal, as long as some form of healing is available (such as one of them being a Bard, or taking Arcane Disciple: Healing, and packs a Wand of CLW). Before that, the casters lack, not power, but durability - both in HP and spells/day.