Ah yes, RNG definitely add "fun" to a job.
We all remember when Lillies where RNG and hated, MCH RNG and hated.

Increased damage RNG would be frustrating when it doesn't proc. Plus we already have the critical hit and direct hit.
RNG control (slow/stun/root) doesn't work. What happens when you want to stun something? You use a stun.

On top of that, stun has a resistance mechanic. The more you stun a target, the more resistant to stuns it will be. By stunning randomly you could screw your group, sometimes you need a stun at a very precise time, not before not later.

RNG is a bad idea, it will be frustrating when it procs and you don't need it and frustrating when it does. Especially when it's utility, even more when it's additionnal DPS.