The only issue I've seen is that the AI is coded to focus fire your lowest AC character, which results in the wizard getting steamrolled in nearly every fight with next to no options to protect them.
That said, once Gale had Mirror Image he became incredibly powerful. He was instrumental in multiple later fights against the more deadly underdark opponents. His damage output vastly eclipsed anyone else in the party when he blew all his spell slots for damage. His frost cantrip was incredibly valuable in soft controlling enemies and his Sleep spell single-handedly turned the sides of several fights that would've been a loss without him.
He even had a bunch of healing spells from scrolls and could, if he chose to, be a better healer than Shadowheart just by preparing the right spells for the day.
Wizards are insanely versatile and their sheer quantity of spell slots make them terrifying.
