Rengar : Why did he have to change?

I just can't wrap my head around why they changed Rengar so much. He is so underpowered now, it's ridiculous. His Q and passive changed a lot but the passive is my biggest complaint. Rengar's Ferocity goes away after you leave combat now, now his buffs from Bone tooth Necklace are completely different and I preferred his original so much more, and he has to get unique champion kills now in order to get stacks of his necklace (which makes it, at least for me, harder to get to The Hunt that begins between Kha'zix and Rengar). I'm not sure if Riot Games looks at these posts but I figured I would post it anyway. I can understand changing Rengar but, he has changed way too much. &