People play hundred of games and are still in silver.
Doewnt matter how many mastery points they got, 5000 or a million.
Bad is bad.
Also most champions are very simple to play and doesnt really require many games, even if you first time a champion youd likely get the hang of them within the game.
You just need to know the build path and farm up.
Also the player could be a smurf and every game would be a 'first game' with a champ depending of they switch champs a lot to climb.
There are a lot of nuances to 'first picked champions' to claim we should permaban players for first time picks.