IMO, her kit is overloaded.
When you think about an ultra long range marksmen who has a huge steroid and a kit built around sieging/melting objectives, you assume she's going to be vulnerable to being dove. Sort of like a siege tank in SC (or like Kog, TBH).
But for some reason, Trist is one of the safest marksmen in the game (besides Ez). The longest range marksmen in the game doesn't need top-of-the-line escape and self-peel. There's no reason for her to have a huge RESETTING jump in addition to massive knockback on her ult.
I'm not an expert or an analyst. But if I had to guess, the only reason Trist isn't pick/ban is because the meta has become so safe for ADCs in general. With ardent/enchanter meta, and assassins/divers being weak, ADCs are extremely hard to dive regardless of who they are. So raw DPS is favored over safety.
But, in a less safe meta for ADCs, I think Trist is too safe. Esp. for solo queue.
Azir literally just got a mini-rework because Riot thought that a high DPS champion with good mobility and self-peel shouldn't also have long range. Doesn't that also describe Trist?
Riot needs to decide what her core strengths are supposed to be, then double down on those and cut away some of the random strengths she brings to the table.