Every ranked Y ban Rengar because You don't know how to counter him. Man he is a champ that is usefull 1 time every 150 sec until liv 11 and y can't deal with him?? I don't think so. Y can counter his ult having vision on him, staying in group and buying a pink, then His R is just a closegap out of bush. Don't call a champ broken, just because you don't know how to counter him.
Now rengar has tons of counterplay, just the fact that he is more visible in ult then when he is in a bush...... just the fact that he need to collect 5 stacks to do something with his ult and not just press R to oneshot someone. Rengar's R can be use only to engage, just for this, you can ask for a nerf