obviously they are gonna name the obvious things and not how to lane againt her. every squishy champion is squishy. you can't call it a weakness. ap fizz is squishy. zed is squishy. they do damage. they don't tank. let me name weaknesses other assassins have
Rengar. immobile and he will kill you but he can be killed because has nowhere to go
Talon . same as rengar
eve- same as the two above
kha zix- unreliable escape similar to the two above
fizz- he has his E but then again his combo is much more predictable giving you time to react to exahust or flash
zed. i guess similar to fizz but more mobile with his W. annoying
leblanc. chunks half your health with 1 dorans ring. hell did you watch msi where an lb with 2 dorans ring 1 comboed ryze under his turret. UNDER HIS OWN TURRET. he had 100% health. she 100-0 him under the damn turret with 2 doran rings
there is no counterplay in terms of laning. the only thing you can do is if your team is good enough to cc her midway in her dash or something or just pile on top of her when she appears. other than that she has no counterplay in a 1v1 situation other than that i hope she doesn't 1 combo me in half a second because you can't kill her faster than she can kill you. you just hope shes not good.
her weakness is the basic weakness of any assassin. bad at team fighting around tanks. which is nothing special about her. every assassin is. unless she obviously nuked 2 people before the fight even start. watch pro play. shes the only assassin consistently picked over and over again because she lacks counterplay and you know what shes gonna do but you can't react to it fast enough.
what is the last time you saw talon rengar or kha zix in pro play. i saw one kha zix that was so bad makes you cry. a rengar that went full tank. and haven't seen a talon yet. its just leblanc. and zed sometimes but even zed has more risk reward in his fingernail that leblanc has in her entire kit.