Current MMR creates consistent negative experience?

Disclaimer: This is obviously anecdotal from my group's experience.

We have an average group overall that fairly regularly plays in a 3-5 stack. I also play fairly often in solo queue. We have one above average player, two experienced MOBA players, and two competent newcomers. Overall, we had a lot of fun with a winrate well over 50% for the first week or so. Then as the game picked up steam, we noticed our winrate going down. Every once in a while we would still get a small win streak but far less often. Now we lose almost every match we play in, and I honestly don't understand it. Our winrate is probably around 25% which is just not any fun to play. Yesterday between some solo queue and various small 2-3 stacks I lost 8 or 9 games straight. This is the quote about MMR for early access:

Your hidden rating will be updating based on the number of games played, skill level of opponents and your win and loss streaks.

If this was implemented properly, it sounds pretty good. Should end up being fair games and ~50% winrate accounting for random chance. I am not an expert but with that much of a loss streak I can't imagine any reason to continue to match us against clearly superior teams. The matches did not get easier throughout that day, if anything they got harder. And this general experience is not just from that day, but has become a pattern in the last few weeks. Bad luck is one thing, but this seems to be a larger issue. If we were somehow playing "badly" enough to just lose that much, shouldn't our MMR just bring us down to face equal opponents? Even if we're just unlucky and playing fine, shouldn't it see that loss streak and adjust according to the quote above?

There may be things I've missed accounting for but I'm generally looking for feedback from people in similar group situations or just to hear people's solo queue experiences. I really want to enjoy this game, I loved Paragon and Predecessor is doing so much right. But a poor matchmaker can really make it hard to have fun.