I'm iron 3, went to bronze 1, and back to iron 3 again, so I mostly meet irons and bronzes in all my matches.

So, why do I meet a player that is iron 1 and playing like immortal?

The guy just 1-tapped the whole team and got 36 kills, while our MVP is bronze 1 and got 12 kills.

And to make it worse, the 36-kills guy just was toxic saying my mom is ez after tapping me a head shot with a classic, and I forgot to report him after I raged quit the game.

Does riot detect those players and put them intentionally in low elo lobbies as there no other FIT player to be placed instead?

I got tilted and deleted the whole game from my PC without an intention to install it again in the near future, and I do regret spending money on this unfair game.