Why does diamond rank even exist?

Honestly I forgot about this thread here and was only coming back to see if there's any info on SBMM. Not only is ranked messed up in Diamond lobbies, but casual is a bigger sweatfest than ever. I liked Duos, and some of my friends too, but after it ended we all stopped playing the game and moved on to other games.

I played some ranked matches today on my alt acc which is a gold/plat account and in gold at least the matches feel a bit more normal: You have 2 potato teammates, but you're playing 1vs3 against gold players with some occasional diamond/pred smurfs. Literally the only way the game is somewhat fun and casual is smurfing in ranked smh. Me and my friends believed there was no incentive to smurf in this game, even when they introduced ranked because you could just play casual instead, but now all these decisions are gonna do is make smurfing more prevalent.