I'm not sure on this but I think nerfing both his AD and R is a bit much or maybe the wrong approach. Although, I'll admit that his level 2 and 3 are insane if he can use his abilities.
I'd probably just nerf R scaling and possibly the vision denial (by 0.5 or 1 second) since that's a big part of what makes him strong in competitive. On the other hand, Nocturne mains will be used to a 6 second vision denial window so it could be pretty annoying.
He's tricky because while he does have a lot of gameplay options (splitting, causing confusion, cleanup, even engaging if they're a bit mispositioned), his actual kit is a bit binary. That's OK sometimes but it makes small number changes especially large in impact.
Anyway, take this with a grain of salt since I don't actually main him and have banned him quite a bit just because he tends to snowball a lot.
BTW: I think it might be a bit awkward to have a 4 second lower CD on Tristana E since you usually want to sync that with Q.