Which one is better and which one's the cheap knockoff?
Among Us
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Fall Guys
(https://images.pushsquare.com/85a8ef8f462c0/fall-guys-guide-ps4-playstation-4-1.original.jpg)
I have not played any of these games, but I have watched videos about them on my subscribed channels. Judging by entertainment value, I find Among Us to be better, because it adds suspense, suspicion, secrecy, while in Fall Guys, people can either move or grab. Fall Guys is visually cluttered, and does not allow much flexibility for commentary for streamers. The people playing it usually resort to talking about their past achievements and skin choices, that's how little commentary the game allows them.
This was all about watching these games though, and not about playing them. I cannot answer which one is more fun to play. I do not intend to play these games, because multiplayer games tend to be toxic (people grabbing you, pushing you off, blocking finish lines // people not listening, calling emergency meetings for no reason, "friends" on opposing sides teaming up and gamethrowing for the other team, bad reasoning being correct for the wrong reasons against unlucky impostor, teammates leaving the game, etc), but I love platformers with good controls, so I might enjoy playing Fall Guys more than Among Us.
But to answer the question, none of them is a knockoff. Among Us was created by the same person who made the Henry Stickmin series, that's one thing I know.