Spell damage overall is definitely lacking the way it scales compared to melee abilities. That and staffs do nothing to buff the base dmg of your spells either so they need to fix that (but I don't want them to go early D3 route either which had axes/swords buffing spells because of base dmg on them) so it's kind of tricky.

I think the easiest solution when it comes to spells is to buff the base dmg scaling of the individual skill and allow 2H weapons to have more sockets/affixes.

The willpower regen is atrocious on staff.
The spell damages are not scaling from your weapons but base spell damage.
The +X% damage is not scaling properly on spells (just tested this).
The auto attack on staff is missing more often than not which is even worse for willpower regen.
The animations with the staff suffer from LONG recovery frames & input lags (even worse with server lags).
AOE Spells sometimes disappear just after being casted.

For 2H and the staff more precisely :
They should give more sockets, it's a must.
The willpower regen on staff should be way higher or give them the ability to scale from passive node with +X% willpower regen (based on staff willpower & your current max. willpower).
The staff should have a base +X% spell damage - it doesn't make any sense otherwise, it's a dedicated spell item with no other options so... buff it. And make spell damages scale properly for god's sake.
Make the autoattack register 100% of the time and add scaling for bounces (not just twice and that's it) but more like 2 to 5 times and make it random.
Make the base animation faster and properly increase the +% Attack speed & Casting speed... With a lot invested in this stat it's atrociously low, it's not fun. And fix the recovery frames, it's an ARPG not a FPS Hack&Slash, it should be faster. I'm thinking it's a bug and not an actual thing that was wanted...

I really wanted to make a pure mage with 2H staff but it's really not fun. Especially when you compare it to the other builds or mage archetypes which are working :D