Tbrh, as a Rengar main, i can assure you that since the rework, Rengar is most of the time played as a Bruiser too.
His W have a really poor synergy with Full AD Rengar because no damage mitigation and a heal based on the damage you already taken on a melee Squishy will only help you to survive for like 1-2 seconds more and that's not enought for Rengar.
While Being bruiser with Dead man Plate + Spirit Visage bonus healing will allow you to tank considerably much, use the CC immunity to dive into the ennemy team and not being reliant and your tank to engage.
Still comparing noc shield with Rengar W is totally dumb yeah and believe it or not but full AD Nocturne is actually way better at deleting squishy witn no "counterplay" than full AD Rengar right now.