Pre-made Platinum player vs unranked players in normals - matchmaking is broken

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Just had a game in which I played vs A PLATINUMII player with highest in our team being Silver5. Not to mention he went 25/4 and game ended in 20 minutes as you can see below (Jhin). The Platinum player was pre-made with others, and I'm not saying he is doing anything wrong since this is a normal game. But how can RIOT match make pre-made team with PlatinumII player vs 2 Silver5 and 3 UNRANKED Players? Shouldn't there be at least a gold player in the enemy team?
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