That's not necessarily true though. As a diamond player the first week of the split, I actually gain points when my teammates and opponents are all diamond / master / pred players than I do later in the season (in diamond) when my teammates are all platinum players. That's because higher level players know HOW to play the game and don't make many "mistakes" as you're talking about. If I'm in a pub and I get on a team with two absolutely terrible players, and there is a single master's 3-stack... I'm dead, no matter how hard I play my butt off. My two teammates are a liability.
The mistake is solo queing. It's a team game, and solo queuing puts you at an extreme disadvantage. I would rather be a master's with other master's and preds. Conceptually, it's also more rewarding to fight people who are your same skill level. Maybe you get lucky and kill a pred but that's going to happen 1 time out of 1000. You don't learn anything from that. You learn from being matched with similar skill levels... that's why every sport in the history of modern humanity groups people into skill classes, like football, baseball, road racing.... pretty much anything. You'll never play a game where an NFL player gets groups with a person who plays pick up football in the park (unless it was personally agreed upon by both ppl). This game is forcing NFL level players to play in lobbies with park players because the skill gap is too large to find games for players with a 1.25 k/d. If you have any positive K/D then it thinks you belong playing against master's players.