Rengar's escape, as the bursty, insta-kill assassin that we all know and cringe at every time we see, is quite literally getting the kill.
Coming from the jung and then jumping at the enemy laner and bursting them down is how Rengar escapes. Being able to cloak for a good length of time and walking through the enemy team to find his target is how he does his job, causing panic and confusion similarly to other stealth champs who can burst. He does have Hard cc, his full ferocity bolas is a root that is a fair amount of time a point-blank shot from a fresh jump, and even without ferocity it is a slow.
Liss's initiation relies on her E, which is incredibly telegraphed if Lissandra is visible as it is a slow-moving skillshot. While the skillshot itself moves faster than champions, as far as actual skillshots go it moves slowly compared to others. Being the low-range zone control mage that she is she relies strongly on being able to position herself in the fight. Yes, initiating from the jungle with her E is often very effective but very few times will MOST players use her E as a skill to land damage with from a range as I believe there are not many skillshots that are slower than it, I believe Anivia's Q being potentially one of the few that are indeed slower. The few times you may actually do damage with it are if the enemy is more focused on smacking someone else in their reach or if you're very close to your target so that they are busy standing still or not able to side step it fast enough. Her E is her one engage and disengage/escape skill on a pretty long cooldown and most people don't regard it as anything other than just that, engage or escape. They sometimes don't even regard it as a damaging ability unless it's a dire situation where you have to throw everything out to either get the kill or not die.
Liss also needs to be untouchable for a brief moment. Her role in the teamfight revolves around either helping peel or diving in with her claw into the enemy team to try to make a play. She's a mage, diving RIGHT into the enemy team. She needs a way to not get melted immediately after which is the safety her ult can offer if she casts it on herself. If you want to make an argument about zhonyas then you're going to have to include every mage that has zhonas as a viable item, including fizz, akali, etc. which is an issue with the item, not the champ. It's similar to why Sivir is banned sometimes,she offers team utility even though Sivir herself is not an amazing ADC
If you want to bring LCS into it, There's plenty of Rengar's cancer deleting champs left and right BY HIMSELF by just giving them a dirty look.
