Rengar isn't a one trick pony
So I understand Rengar has made a come back of late, mainly his one shotting assassin style of gameplay, and I also get that it is quite strong mainly in lower elos. But that does not mean that's the only thing he does!
I enjoy playing bruiser and tank Rengar, always have and always will, and he's still quite potent with these kinds of builds, just a different playstyle. What I find infuriating is dealing with simple minded individuals who refuse to admit champs have different kinds of effective build paths! Yes when I get fed and dominate the early game cause I know how to fucking jungle and still build bruiser/tank I get a lot of "I HAD NO IDEA HE COULD DO THAT!" Which can be satisfying, but the problem is that it's a double edged sword. Like, if I'm behind for any number of reasons or even something as simple as the enemy team comp makes assassin Rengar nigh unplayable, and I build tankier to deal with that particular game even my own damn teammates cry and moan about me not being an assassin!
I've even been goofing around in normals, with a build like
and some other tank items, still kill the enemy adc 1v1, and they'll then start harassing me in all chat cause my build is "so bad." I can only laugh at them and keep killing them, but it's still irritating that there are so many people now who think Rengar MUST be an assassin.
Open your eyes people, Rengar has many different options, and sometimes the assassin route just isn't the best choice.

depending on what you need. :)