Anyone here who thinks Rengar is Op has either never played him or doesn't care to look too carefully at the facts. I will now Try to give my point of view on the matter as a Rengar main.
"His ability to heal and deny CC" wrong on both accounts. He doesn't heal in the traditional sense as most other champions where they use an ability and they gain health, he must first take damage and then he has a chance to heal a portion of it back. That amount that he heals is based off a portion of the damage he took. The only time he heals crazy is if he used Normal and Empowered W. This means that he used his empowered ability on surviving, not on "bursting". "Deny CC" - this one is incredibly absurd, Rengar has no CC denial, he only has a cleanse, and its not like a GP cleanse that is on a cool down, its based off of his ferocity, the Empowered W that I was talking about earlier meaning that if he chooses to use that ability he trades out his damage or his CC. Not knowing how to trade against a Rengar to bait out his W doesn't make him broken it just means you do not know how to play against it. In Regards to "Burst" Rengar has about as much burst as Renekton or a Zed in my personal opinion. And that is good, he is an assassin, the only issue I will say is that his damage at certain points in the game are too strong, specifically when he gets his power spike of Duskblade. That being said, I think Duskblade is the issue not Rengar, since the item actually rewards with free damage for no reason what-so ever. Aside from that his damage is fair, if a Rengar builds assassin he will do his job as an assassin, not as well as other assassins I argue but his damage is there. When talking about burst people jump the bandwagon and cry Rengar, but what about other champions that always get overlooked???? Have you never been against a Kha'Zix who one-shots you with just warriors and Duskblade by using a passive auotattack and a Q? Or how about a Shaco with Duskblade and crit?? How is that fair and allowed, but oh god Rengar whose ult tells you he is near is broken beyond measure?
Another point is that you said that laning against him is cancer. Laning against a good Rengar is challenging, as it should be because the player put in the time to master that champion in order to play him in top like that. Do you know what cancer it is to take Rengar top against 90% of match-ups??? Almost all champions in top either outsustain him or outscale him. Most toplane champions like Camille, Renkton, Darius, Nasus, Vladimir, Aatrox, Maokai and others have a for of sustain that doesn't require them to take damage to heal back a portion of that damage back, in turn real healing. Most of the listed champions outsustain you in trades and kill you. Other champions straight up shut you down like Garen who silences you and E's (which does damage over time and you cannot heal his Q burst because you are silenced plus his passive healing is something Rengar doesn't benefit from in surviving the lane), ,or Teemo who deals damage over time and silences you, making your damage dealing ability useless (Q). Or jax, runs you down with his E and you cannot do anything to him until it is down, a smart jax played doesnt fight without it. Another point to bring up is CC. Jax, teemo, Garen, even Darius, and many other champions have reliable and strong CC, Rengar doesn't. His only hard CC is Empowered E and if he uses that, again he misses out on empowered Q which is his damage, but unlike the other point click CC's I just listed Rengar's is a skillshot that can be blocked by minions and monsters so setting up ganks as Rengar is not as easy as most people think it is. In addition, just like Gnar, Rumble, Renekton, and Tryndamare his resource bar tells you when to fight him, its not hard.
I know many people here will probably not read this, since most just jump the wagon to try and get him nerfed, but compared to some other champions out there he really doesn't deserve it. It isn't Rengar who is 90% of the times a win condition late game, that is Jax, it isn't Rengar who can melt anyone and go into stealth several times while having knock-back and true damage, that is Vayne, it isn't Rengar who has Rengar's exact burst but better and an escape and resets, that is Kha'zix. Maybe the champion is not broken, maybe most of you here do not know how to play against him. Most Rengar players that you see are players who dedicated their time and are actually good at the champion, some are who pick up the champion after watching a NightBlue Video but that is not usually the case, the fact is that when you are in a game and the enemy Rengar is 4 kills ahead and 3 levels on you because he played well early on it isn't because the champion is broken, its because the player played well or got lucky off your teammates or your own misplay. This post is not to cry about Rengar's weaknesses or to bash anyone, its just that there are few normal Rengar players, most try him and drop him because they do not do well, if you do not believe me watch one of Yassuo's recent vods where he plays the day before the new season, he enters the champselect and procedes to complain about Rengar because he recently played against Scrubnoob, saying that the champion is busted, he picks the champion and proceeds to turn into the best chef in the world feeding. I implore you to try Rengar out before you complain about him, see how useless he can feel late game in teamfights, how he struggles without real sustain in toplane. Experience how good it feels to outplay someone with bushes and how it actually feels to use ferocity to determine if you want to try to CC someone, to bait out enemy CC or to go for the kill. Try the champion out before you jump the bandwagon, sad thing is I do not think anyone will, most will probably just sit back and complain, but hey you can't change the minds of plats, golds and silvers.