Whats the purpose of flex queue?

It feels like flex queue has nothing at all to do with whos better then the other, it has to do with rolling some dice and hoping you roll high. Some games i have bronze 5s on my team, other games i have them against me. Some games i have high plats on my team against silvers/bronzes. Sometimes its the other way. Im gold so im like in the middle of all those ranks, its easy for me to face silvers/bronzes on the other team, its not easy when i get bronzes/low silvers on my team and high plats on the other team.

How in any way does flex queue determine your skill? This is horribly bad match making. Every time i queue up i just have to hope i roll high on the dice, which seems really unfair. At least in other queues i got people my own rank(except for the few times im with/against boosted players)but now its just insane.