Trist is a lategame hypercarry. It's her job to destroy your team late game. You know, like Vayne. She has the tradeoff of being mediocre early and midgame until she gets some items and gets her passive range.
Why is Riot repeatedly nerfing anything that's popular regardless of whether or not it has counterplay.
Because her early game is not bad enough for the late game she has. Compared to vayne, who is always easily catchable, squishy, etc. Trist is hard to catch, and while squishy, can often pop people before they can get close enough to gapclose. She needs some serious early game nerfs.
Just so you know, 2.5% attack speed per level is the same as Vayne who is also a hyper carry.
Early game she compelty shreds you, and with that jump it allows her to disengage easily mid game.
Because they buffed the shit out of her several patches in a row. She's too strong right now.
Tristana got so many buffs and item changes made her extremely favorable and her "mediocre" early and midgame is pretty much nonexistent. She trades early game very well with no manacost on Q and constant DoT and Greivous Wounds on her E. Not much of a reason to not pick her when she's open. Only ADC that can deal with her consistently is Lucian
pretty much what everyone else said you can dominate a trist in lane as much you you want as soon she's got a 
+
or 
she just dominates her aa is ridiculous late game she's the only adc with a reset (her W) not to mention her base stats are better then most hence and ever since the item changes mostly for adc you can't sustain her damage anymore even late game vayne as a hyper carry has risk + reward mechanics while trist sits on the back line pops a Q so long story short she needed the nerfs
They should nerf her.
