Why is flex so broken?

As a silver player who's been silver for a couple seasons, it seems like flex only caters to Plat or higher. Literally every game I play is against a couple diamonds or plats? AS A SILVER. And I've been told you get an mmr penalty for playing in groups....In a gamemode made for groups????????? Will not be playing flex anymore, I'll stick to solo/duo or non ranked. The steamrolling in flex from diamonds and plats makes this game mode unbearable.