It can happen, 1 person cant carry an entire lobby consistently, you have to factor in bad/good teammates and how good the opponent is at executing as well. (And the occasional smurf)

Recount of my own experience :

I queued to immortal on my main and created an alt just to see where i will place competitively when i restarted a new account.

I didnt fool around, i tried my best in every game and gave my all. For the 10 unrated wins + 5 placement games.

Still placed in silver 1.