Underpowered? O_o
I picked staff for Gale and i must say i was never more satisfied with any other weapon in his hands.
Especialy since you get 1 charge per magic missile (or other multitarget spells, if you hit ... shatter is also quite good for powering up). :3
You get +1 to hit, +1 to damage (or 1d8 if you have 5 charges) ...
(The only let down here is that if you have 7 charges for example ... they all expell at once, with no futher benefit.)
And with other items to that set also +1 to armor and saving throws, and +3temporary HP (wich i mostly use to keep my Armor of Agathys up)
I never had feeling that is is anyhow weak ...
I mean what other staff do you use with your Wizard? O_o
Bless staff is also great, true ... but only once per Long Rest.
