When you queue with a 5 stack you should only go against 5 stacks or at least a 3 stack and a 2 stack
The matchmaking is so bad rank means nothing I'm currently plat 3 and get into games with as low as silver and as high as master while im solo queuing.
Along with not being able to lose a Rank tier by law of the universe eventually if you just play enough games you're gonna get lucky and hit a rank you dont deserve because you lost 200 games in a row just to win 17 games in a row rinse and repeat play 1000 matches and you're in masters.