I think the simplest way to fix it would be changing up the staff, and making the scepter’s projectiles move faster.
I find it strange that the staff’s primary attack is a weak fanning AoE when its one handed counter part, the scepter, is so single target.
Honestly I’d rather see the staff switch to more PBAoE support skills with enemy debilitating/burning side effects, and a single target channeled primary attack.