cait is quite a bit over the top imo.
However, tristana still has a couple of advantages. she's harder to catch when pushing sidelanes with the high range on her W and the aoe-knockback from ult, she has better selfpeel vs most assasins IF they get ontop(which is harder to do vs cait and her traps).
Earlygame, i wouldn't say tris is weaker. She's less save, but has way harder snowball potential. Her early all-ins are probably the most potent of any marksmen and with a cc support like leona, tris can become a very potent kill-lane.
She also has way better 1v1 than cait in the mid and higher(active) solokill preassure through out the game, she can actually force things while caitlyn can only play the long game. Also, tris remains the fastest towertakeing adc and still has the cleanup potential that cait lacks to convert a won fight into a straight ace.
However, while she has strong snowball potential, tristana also has a realy hard time catching up if she falls behind early, she lacks ranged waveclear/far options and can't contribute to early/midgame fights without getting quite a bit close, and once in combat distance her W is actually a rather weak escape due to the awfully slow animation.
So all in all, tris is not that much weaker than cait, but she works differently and is more of a high risk, high reward pick, while cait is more the 'slow and steady wins the race' type, with right now a bit to much reward for how low her risk is(mostly the 5traps and the insane damage of her empowered headshots)
