Honestly he just needs to be reverted. As it stands now Rengar top lane has far too much healing and consistent all-ins. Before his rework he needed 2-3 jumps to reach full ferocity since it was 5, now he only needs 4 ferocity AND he gets one stack just by using his passive jump.
Additionally, his W heal is so much more unhealthy now as grey health is just an unhealthy mechanic, especially for top lane. On top of all that it's a cleanse when used as its empowered version. Before the rework his W just granted resistances, with his empowered W being a flat heal (which wasn't that large to begin with).
Oh, and he gets free movement when using an empowered ability now, great rework lmao.
I would also like to add that this isn't just a Rengar problem, almost every single top laner in the game is extremely oppressive, with worthy mentions going to
just to name a few. The new runes just make it far too easy to kill your lane opponent in one rotation, or in Rengar's case, whenever he wants since Grasp/Fleet grant him access to a large amount of sustain to pair with his W(s).
His passive isn't actually the problem, you can punish his passive extremely hard, the problem is that he gets ALL of his ferocity from one jump any time after level 3, as well as the fact that runes are overloaded.