Saruman magic, unlike Radagast, can have an uncapped area of influence.

Radagast magic requires deep trust, which is hard to authentically create at a distance.

Saruman magic can have its area of influence extended, gaining more leverage.

Simply insulate yourself from any disconfirming evidence or personal challenge, surrounded by sycophants.

Saruman magic works through the absence of self-doubt, so build walls to prevent doubt-causing information from reaching you.

But disconfirming evidence, challenge in relationships, is what makes us grow, what makes us human.

So to wield this magic at scale makes you ever more of an emotionally stunted monster.

Less and less of a human.

A deal with the devil.