There's been a lot of outrage on the boards (rightfully so) about the matchmaking system and how it seems like the system is designed to force you to a 50% win rate by giving you worse and worse teammates the more you win.
Whaat? That's totally not how the system works. The system gives you better and better not worse and worse partners the more you win, both in your team and in the enemy team. In fact, you said :
Players would be matched off their elo so that both teams would have equal combined elos and so that lane opponents would be the same elo, within a certain tolerance.
But the first part is already the case, and the second part is impossible to implement (just take a few minutes to think about a few ways to game the system and see how you would go about trying to minimize them, I'll watch).
So say your ELO is 1000. You're matched with other people at around 1000 ELO. Then you win a bunch of match, and you get to 1200, so you're matched with other people around 1200. In both teams, not just the enemy team. You get better teammates on average.
But you also get better opponents, so you'll win less games. And if you got a lucky streak and you don't actually deserve 1200 ELOs, you'll lose a bit more than you win and you'll get down to 1100 or something.
The system forcing you to 50% winrate is a myth. The goal of matchmaking is to put you at 50%, but that is not how it actually performs the matching. It simply tries to match you against opponents (and teammates) of the same level as you, so you should naturally win 50% of the time.
All this misunderstanding comes from the fact that matchmaking doesn't actually know your true level of skills, it just has your ELO as the best information available. If you get a win streak and you get your ELO higher than your real skills, the matchmaking will give you matches too hard for you and you will lose, but that's fair, because you actually deserve to lose ELO.
And the system most definitely does NOT gives you bad teammates to force you to lose! Just try to see the situation from the point of you of every player. Because in your scenario there are three kinds of players (you, unfairly screwed; your bad team; the good enemy team) but for the system there is only one kind of players: those it has to match in order to create a game.
If it wanted to force a loss on you because you had won "too much", who does it put in the "bad team" with you? People from lower ELOs that are at 50% winrate? But why would it punish those players and give them a free loss? And who's gonna be in the "good team"? Because these lucky guys just got handed a free win. Who does the system should give this free win too?
Whatever way your turn it over, it just doesn't make any sense.
From personal experience when I was silver 1 trying to get into gold last season I was being matched against players who were gold 3 to platinum 4. Why the hell should someone have to beat high gold or low platinum players in order to get into gold 5?
If the system matches you against Gold 1 players (or gold 3 to plat 4, I don't care), it means the system think you deserve Gold 1. If it's right, you'll win 50% of your matches and all is nice and good. "But what about my Rank, it only displays Silver 1?!", you'll say. Yes, but it will still climb. You will only win 50% of your matches, but you will earn something like 30 pts per win, lose 15 pts per loss, and over 10 games (5W-5L), you'll have won 75 pts, almost a full division. You will climb. There is a little problem with Promos but I'll come back to it later.
But what about if the system is wrong, you don't actually deserve Gold 1, you just deserve Gold 3? You'll lose more than you win, because the system overestimates you, but you still deserve to be Gold, and you're still stuck in Silver. Totally unfair, right? ... Except you're not actually stuck. Over 10 games, you'll do something like 4W-6L, but with 30pts/win - 15pts/loss, you'll still get 30 more points in the end than when you began. You're still climbing, even with a negative winrate. But since you are below 50%, the system will understand it was overestimating you, it will correct your rating, and for the next 10 games you'll be matched against Gold 2, not Gold 1 anymore. Still too strong for you if you only deserve Gold 3, but every game you play the system gets closer and closer.
In the end, all is nice and good. (Problem is, "the end" is "after everyone has played a few hundreds games", and a lot of people don't play so much, so in reality, all is mostly nice and good with a few quirks sometimes.)
The problem with Promos: if the system correctly estimates your level and gives you a 50% winrate, well, you are kind of stuck with Promos. Winning a Best-of-3 means getting a 66% winrate, and a Best-of-5 a 60% winrate, and you can't do that with a system that gives you 50%. So the system I described above kind of screw you with Promos. But there are 2 factors that alleviate that: first, that's why Promo Helpers were introduced. With Promos Helpers, you need only 1 win over 2 matches for Bo3 (exactly 50% winrate), and 1 win over 3 matches for Bo5 (barely 33% percents), so you can pass them easily. Second, even without Promo Helper, we're talking about averages here. You may not get your Wins in the right order to actually pass the promo the first time, but with enough tries you'll get it, and when you're into the next division, you can start rocketing through league points right away.
