Why does Flex 5v5 Ranked not take into account Solo/Duo MMR/Rank as well?

Hi, I'm unranked in Solo/Duo (ended Bronze 2 last season), and have less than 25 Flex Ranked games this season played. I played in a 5v5 last night with a group of friends who are all low Silver-high Bronze in Solo/Duo and Flex. Why am I getting placed against an enemy jungler with 200+ games this season in Solo/Duo and is Plat 5, and an AD who has 400+ games in Solo/Duo ranked Gold? I'm not even super angry about getting trashed, I just genuinely want to know how we get placed together. Our team's collective MMR isn't that high. Why are we getting placed against a player who is statistically in the top 6.9% of players on our server? Why does it not take Solo/Duo rank into consideration a little bit? If this was what was just recently marketed as the queue to play to practice for Clash, as it was, I think it should have similar matchmaking: i.e. taking into account someone's highest rank on Summoner's Rift. This is absurd. It wasn't even like matchmaking broke because our queue time was so high it just said "find any opponent and slap them together." It was an instant queue pop, 0 seconds.

First the terrible jungle changes actually go live and now this x d