IMHO a moon druid is just insane OP. Reasons? A) Flaming Sphere which is the most OP spell in game. B) Bird shape.
Wiz can learn flame sphere
But yea i do think moon druid is one of the strongest solo builds right now.
My favorite solo build is a dwarf / gith wizaard. Low intelligence - spells are mainly Buffs, utility, or magic missle - things that don't need high intelligence. While you dont have a ton more weapon choices, the racial weapons (axes or swords) is way more than base wizard.
14 Dex for the natural medium armor from gith or dwarf. High on STR / Const.