Honestly, Just Gut Leblanc's W Damage
I love LeBlanc, and I think she should be able to 100-0 squishy targets, but it should require her to use her Q / E combos rather than W cheesing.
Seeing people max W and spam her ult'd W and still deal enough damage to assassinate targets is aggravating, as it has essentially the lowest amount of skill necessary. Her Q and E do more damage, but only if both parts of the spells proc, while her W has more upfront damage and no combo required.
Her mobility spell shouldn't be a viable 1st skill max or have the same base damage as Lux E or Orianna W for example. Additionally, maxing it first allows her to somewhat negate her poor waveclear, as it's her only AoE ability.
Suggested nerfs: W: 85 / 125 / 165 / 205 / 245 (+ 60% AP) -> 80 / 100 / 120 / 140 / 160 (+ 50% AP) Mimic W: 150 / 300 / 450 (+ 75% AP) -> 100 / 200 / 300 (+ 60% AP) New effect: W applies a mark to minions, this mark is detonated by any damage dealt by LeBlanc and deals 20 / 40 / 60 / 80 / 100 (+50% AP) damage to the minion. Mimic W increases this damage by 100%.
The new effect would make up for her reduced waveclear capability, but would be more time consuming unless she uses her ult.
tl;dr: Nerf W damage, require LeBlanc to properly combo to kill her targets.