5 stacks only become problematic the more skilled the team is, a 5 of gold players aren’t going to do great into 2 Masters and randoms as an example, I’ve faced that before twice in the row.
You get 3k+ MMR players in one party and because the 3k+ party is a low population you queue into randoms who are pretty inexperienced if not NEW to the game.
I wish 5 stacks would at least wait a little bit more and refrain from matching Duo which is one of the most common matchups.
Reminder: It has been proven that 5 stacks vs 5 solos are heavily refrained in the match-up entirely (it’s almost 99% none-existent).