Everywhere. The game is scripted and repeats on a loop. Everything people do is doing the exact same dance again and again and again. Nothing changes, content gets old faster, and the difficulty in challenging content has to be ten times more punishing to ensure people do not do a single mistake else they get body checked. I have never trained to be a professional ballet dancer, but it sure does feel like I'm using a simulator for it, and in casual content, it's just pushing squares into squares and triangles into triangles, and there is not even a single variation in which order. RNG in encounter design and instance design would bring back more pause and breaks, and potentially encourage more multiplayer interaction beyond "hello / thanks for the party".

That was for encounters.

Now then for jobs: I said "positive". What's positive? RNG that does reward and doesn't frustrate. In opposition, negative RNG would be RNG that only brings frustration when not yielded the expected result.

Positive examples: simple skill procs, rng Fang & Claw and Wheeling Thrust proc order, Thundercloud (before a legion of sharpcast), AoE dots generating procs on old bard, Dark Dance on HW DRK, randomly induced busters and the likes that can be actively countered by defensives yielding beneficial procs (TBN style, just without the break requirement), etc.
Negative examples: minor arcana (damage vs heal), quick synthesis, old ARR/HW accuracy, etc.

I'm sure there is tons more to talk about here, and I know I'm probably asking for a total paradigm shift, but that's my tastes and my feedback.