His gun is designed specifically to be bad outside of the hook combo.
So his gun isn’t the problem.
Hook is, and there’s two ways to go about fixing it.
- Make Hook easier.
Allow him to throw the hook more often and be a bit more generous with aiming it and things would be fine without touching the damage on his gun.
Or
- Make Hook more rewarding.
Increase the damage Hook does itself and add some kind of debuff or debilitating effect to the hooked target that lasts a bit afterward.
Those are your choices without completely reworking his ENTIRE kit and changing his gameplay from scratch.