Is ridiculous. It's interesting, but damn stupid.
Usually when Riot make hidden passives they are so miniscule that they are hardly noticeable, but this one gives one of them a huge advantage.
If they're on opposite teams in ranked it's simply too game changing and luck based.
One team can be losing badly but the Rengar gets an assist on Kha-zix and snowballs out of control, changing the outcome of the game entirely.
Disable it in ranked at least, sick of spending time trying hard to win only for one side to gain a huge advantage for no reason.