Is it just his ability that you can combo to one shot or that's just how OP his ult is. I've always do half health of the enemy team when I ult to them but it's just a matter of fact that I can ult those squishy champion like the ad.
His ultimate is used as an engaging tool on squishies, but his combo itself also benefits from the ferocity recharge on his ultimate. People use this to pull off rapid combos in succession to get insane amounts of damage in a short amount of time. The reason why Rengar can insta-kill squishies late game is because good Rengars generally build a lot of crit, allowing them to hit insane levels of damage every auto attack.
