One thing I find myself doing a lot is going back into fights with this old Leblanc even when I have extremely low health, because she deals high burst in short timeframes. I really like the "sudden death" kind of playstyle this brings. I think to myself: "as long as I play this skillfully, I can burst and get out alive", and my target will just slam their keyboard in disbelief :)
Perhaps you could add a bonus passive for Leblanc -> Ignores 0.6% of magic resistance per 1% of Leblanc's missing health? I like being super squishy on Leblanc, but having the burst to boot (it's deceptive in its own way).