Champ bugs/balancing required [GAMEPLAY]

So I just played a game where a Rengar was the only person on their team that was a little fed. When it came to late game even though he had NO defensive items whatsoever it still took at least 10 basic attacks with abilities of the fed as ADC to be anywhere near killing him, where as Rengar could do 1781 damage with only 1 BASIC attack without using any of his abilities already using his ult on another champ and without leaping from any bush just stood there and hit ONCE with a basic attack WHILE 4 of us was fighting and focusing him, killing the fed as crap ADC in ONE basic attack.

I'd also want to point out a bug where when Rengar ults and he teleports, sometimes there is no exclamation mark to warn you, it was early game when i had just gotten to level 6 as the ADC, Rengar didn't have any boots or any items to boost his movement speed whatsoever yet no exclamation mark came up. I even had my support infront of me to check it out first but there was nothing and he still jumped on me without any exclamation mark.

it frustrates me that champs that have nothing wrong with them are being 'fixed' when these champs need to be balanced. I'd say having Rengar lose half of his stacks on his bonetooth necklace passive on death like it used to be would be a big leap into making him more balanced. Before you could shut him down from getting the higher stacks but now he freely gets them if he's been apart of a kill with no way of getting rid of them. It's just like giving someone a Sword of the occult or the mejais without having any way of losing the stacks.

Another example would be Darius, his pull animation does not go as far as what the spell actually goes or indicates where it does go.

The cooldown on Wither for Nasus with just the frozen heart with Wither maxed he can put it on you straight after the previous Wither ended even with Tenacity. Longer cooldown later game would help fix that.