MMR
I think I've figured out something about how MMR works. You gain less when you duo with people worse than you and also lose more when you lose when you duo with people worse than you. Meaning that, if you want to get a good win percentage, it actually does pay to keep duoing with people worse than you and it'll hurt your win percentage if you duo with people better than you. Don't believe it? Check this out:
I have 106 more ranked wins than losses this season. So you're probably expecting me to be diamond or higher right? Nope, I'm only gold III. And I've almost never dodged or gotten decay from inactivity. You think I'm just a special case? Well also consider this. My main duo partner that I've played oh so many ranked games with this season has a whopping 80 more losses than wins. So you expect him to be bronze right? Again, wrong. He's actually in silver.
Thinking about this, it really does make sense that it would work that way. Tbh, if you're way better than everyone else in your game, then you really don't likely learn much from it, regardless of the outcome of the game. But if you're way worse than the other players in your game, there's a world of good knowledge for you to gain from the game, little matter whether you win or lose.