[CLIENT BUG]? What's wrong with matchmaking in teambuilder?

tl;dr: Why do unranked players continuously get in teams with gold/platinum players in teambuilder?

I think this is better described with how I am experiencing it as it's as much a community issue as a technical one:

So, I'm an unranked player and only play a few games a week but I am always trying to do my best and improve my play. I usually play with friends, a few of them are in silver and I can usually compete more or less equally with them when we play 3v3.

I'm trying to focus on a single role or two (mostly support) to better myself and the teambuilder seems the perfect tool for that. The trouble is, for a long time now, I'm being matched with ranked players in silver, gold and platinum (both my team and the other). As soon as my team realises I can't keep up with a gold / platinum opponent, the harassing starts. Name calling, cursing and other hostilities to no end, including blaming me for their own mistakes. Fun times, indeed. Usually I ignore it but I can't help get affected by it and it's ruining everyone's fun.

I always stay civil, either ignoring them or asking them to either help or calm down (maybe encourage them to read the Summoner's Code), though it rarely helps. In some games after the loading screen where it's obvious what rank people have, I've tried telling my team that I am in fact an unranked player and asking them to set their expectations accordingly. Usually this helps a bit but not always... but it shouldn't really be necessary to do so, right?

But in the end I can understand their frustrations (though not their immature inability to handle the most basic social skills). They want to win the game and get frustrated when someone on their team performs worse than they would like. And that's why I'm asking if this isn't a bug in the teambuilder matchmaking? It's ruining everyone's game that a lowly unranked player gets matched with gold and platinum players, and while this isn't ranked, I really think the game should try and match the players' level with their team and opponents too. Maybe the other team has an unranked player too to even it out but if they're generally winning they're not complaining or having a bad game because of him... unless the tides turn. I really can't see how matchmaking like this is any good, especially when so many players are awful at coping and helping others.

Finally for a bit of more or less hard facts. It seems it only happens in teambuilder and pretty much every game. In coop or normal unranked I usually don't have the issue. When I join as a support in teambuilder I rarely wait more than 5-10 seconds. I have a theory about teams looking for a support might have waited for a long time, and as such the criteria for matching players have softened up over time, eventually broadening the search enough to include unranked players. However it then ignores my very low wait time and should-be much narrower search criteria (I hope this makes sense). Maybe this could be a place to look for improvements in the code?

Cheers