Rank makes no difference to the damage output of the champ.
Her being 4-0 before you ever interacted with her (And 12-4 in the end game) and having near perfect cs does make a difference though.
She clicked 4 buttons while performing mediocre in lane
4-0 with high cs isn't a good enough lane for you?
She didn't outplay anything with challenjour mechanics.
No she probably didn't, but she is a very decision oriented champion. Do you know who makes really good decisions? High elo players, as evidenced by Leblanc's winrate in bronze vs Diamond.
https://i.gyazo.com/7865890026fac31dd53b529e6472d826.png
Bronze
https://i.gyazo.com/e71a8e56df86bd2bb2cc8ad0733703a4.png
Diamond
At worst that is a 4% difference, at best its closer to an 8% difference.
EXACTLY the reason that AP Shaco got nerfed.
He actually got nerfed for instantly killing from stealth, for Leblanc to kill at level 9 (a VERY early gunblade) without passive (a 1.5 second delay) you would have to be so far behind that 907 premitigation damage kills you. For comparison a level 7 Vayne would have 901 health with ~45 mr reducing the damage taken to 625.
Oh that burst we discussed, did you know that 26% of it comes from gunblade? You think maybe that could be what's broken? She was/is up for tweaks, but as is as long a gunblade stays like this she isn't going to go anywhere.