When the fuck does Leblancs damage "fall off"

When your team builds magic resist like they're supposed to.

She doesn't "fall off".

Your teammates' damage just caught up to hers so she looks like she's "falling off".

LeBlanc doesn't fall off because her damage scales poorly - she one-shots well into the late game until the squishies buy Banshee's. She falls off because as the game goes on her damage becomes less and less meaningful of a contribution to the game and there are champions who can do more than just 100-0 someone in 0.33 seconds and then... nothing for a while.

Don't expect her to just stop killing you at some point, expect her to get weak enough that having that potential isn't enough for her to be strong.

When you don't feed her. She is item dependent, so if you don't let her get kills, she's not really useful until late game (where she is also very squishy)

I don't necessarily think it's her damage that falls off, it's that she falls off, she can only take out pretty much one target, and if she fails or gets cc'd in the process she's screwed.

Fun fact.... Leblanc can 2 shot with her W while at LEVEL 1 literally.

Hit W twice, ignite=dead Ezreal. Just at level 1.

its around when 5 ppl have banshee's veil lol. tanks/bruisers will be getting free base mr per level in addition to mr items and supports with aegis and cruciable so it eventually becomes harder to just derp in and kill who you want in one skill rotation. but it doesnt fall off to the point that you auto-win vs leblancs after a while. if you feed leblanc and other champs like pantheon, it will be a while until you can deal with them and you may not have anything left standing in your base if they do their job. the "fall off" is mostly just in relation to other picks like

Level 19