Basically, that. Once my MMR has hit ~Plat 5 I'm matched up with genuinely boosted people - not always, mind you, but too often. And by MMR ~Plat 5 I mean that even though I'm in G1, my teammates tend to be around high Gold to low-to-mid Platinum. Some of those are good, better than I am, in fact. Many, however, seem to know as much about League of Legends as I do about the sex life of wild potatoes.
For instance, in my very last game, we had a toplaner that didn't underperform in terms of KDA and cs as compared to the rest of the players in the game, had an AWFUL decision making, along with his premade (the support). They blamed me for a shit ton of things over which I had little to no responsibility, which made me think there were other players in the premade as well (if your jungler dies 2-3 times in a lane where you were winning in early and then you lose your turret you tend to blame him, and he didn't). After the game I checked his profile because I was curious how someone with such poor understanding of objective control, rotations and such (compared to mine, and I'm only in Gold 1, so imagine how bad he was at that) was matched up with me, because, tbh, that poor of a level was a first for me in this elo.
Turns out that person is currently unranked but was Diamond in last season. Here's the funny part: out of his last 20 ranked games, only 3 were victories, and they span over a VERY long period of time (you can see up to June in his match history). I take it this one was legit boosted then, probably got someone to get him to Dia X and then got a damn long losing streak playing in that elo up until this point. My question is: WHY would people play on accounts they had others to boost for them if the elo where they're at isn't theirs? Aren't they going to end up dropping back to where they belong? Why screw everyone like that, by forcing people to play with your unskilled self (as compared to your teammates)?