I really think that small changes would improve these heroes. Increasing slightly the damage or reducing slightly the cooldown of Saruman's and Gandalf's powers
Correct me if I'm wrong, but I think the problem there is due to a bug, which doesn't increase the damage of the two wizards as they level up. It should be fixed in the next version
About the Witch-king, I agree that his role as a Mass Slayer should be more prominent (actually, Zaphragor covers that role much better), but I don't think that giving him a weapon toggle would be a solution. Maybe increasing his area of effects of normal attacks would be a nice improvement
ABOUT GALADRIEL
I must say that her role as a supportive hero (or a destroyer when she gets the Ring) is quite perfect. However, the fact that she can die against an ordinary Cave Troll or Gorbag is quite lame for her, being one of the most powerful beings in Middle-earth
So, my solution would be to replace her stance-system with a special ability: activating it, it makes her switch to her "Terrible Form", where her role is more centered not on killing enemy heroes or single units, but rather weakening them and disrupting them. Why this?
Because we all know that Galadriel in the Third Age has some sort of "dark side", which shows up throughout her Terrible Form. Thanks to this, she can use her powers in a more darker way than the ordinary support: in fact, in her Terrible Form she was able to banish Sauron from Dol Guldur. But we also know that her Terrible Form is temporary. So, when she switches to her Terrible Form, she can't go back to her normal form immediately, but she will autonomously after some time (which becomes longer as she levels up) and, once returned to her ordinary form, she can't take her Terrible Form for the same amount of time
In her Terrible Form, her attacks will be centered on disrupting units and heroes. Therefore, she can't attack buildings, but her ordinary attacks now weaken struck enemies (similar to the Nazguls debuff) and will knock them down. Her abilities will be the following:
1. Gaze of Terrible Galadriel - ALL nearby units and heroes will have -10% damage and armor. Enemies struck by her ordinary attacks will be weakened by an additional -10% damage and armor malus, and will be knocked down. Passive ability
2. You have no power here! - Resets the counters of the chosen enemy hero's abilities to "just used" (same effect of the Witch-king's ability). Requires level 4
3. You are formless! - For a medium period of time, the chosen enemy hero will deal no damage. Requires level 7
4. Foundations of the earth - It summons a small earthquake on a nearby building. Galadriel's old classic. Requires level 9
5. Banishment - The chosen enemy hero will be instantly teleported to the closest allied base, and will be unable to do anything for an extended period of time. This ability has a long cooldown, and it's a mighty disrupting ability to compensate for not being able to use Nenya in her Terrible Form. Requires level 10
(Of course, using her abilities in her Terrible Form activates the cooldown of her ordinary abilities, too)
WHAT HAPPENS WHEN SHE REJECTS THE RING?
Rather than her Terrible Form, she can switch to her Holy Form, mantaining the same effects and abilities, but with a different visual aspect (if previously her powers were due to her "dark side", now they're boosted by the Valar themselves). The only difference would be in the first ability, which will be the following:
1. Gaze of Holy Galadriel - All nearby enemies will be weakened by a -10% damage and armor debuff. Enemies struck will be weakened by an additional -10% and will also be knocked down. Allies in the radius of her attacks will be healed
All in all, the ability itself doesn't change so much, but given her increased stats from refusing the Ring, as well as the healing factor when there are allies close to her targets, will show even more the awesome powers of Galadriel