Everyone falls back to the old “it’s just as likely for the enemy team to get a bad teammate” defense, but you and I both know that’s not true. I do a lot of PvP in FFXIV as well and let me tell you… Despite both of you having supposedly the same odds, you will often see the same bad player on the same team while the same good player is on the opposite team, due to matchmaking. Now, the game itself doesn’t know this player is bad or a thrower. They just see you both as gold, plat, whatever, so they don’t see a problem with putting them on your team.
This is where the issue is created. You have this idea of what matchmaking should be and what matchmaking actually is. Unfortunately, these are not one in the same. Now, again, if we lived in a world where matchmaking was perfect, then sure. I could say that both teams have even odds of receiving a bad player, but sometimes that’s not the case.
Also, just because you managed to climb from silver to diamond doesn’t necessarily mean it was because of your performance. While your improvement did have an impact on your climb, you also have to think about all of the times that you got a competent 3 stack or duo on your team that helped you win when you weren’t performing well while the other team’s duo or 3 stack wasn’t performing as well as your own. This is exactly why your defense falls flat on its face because you’re wanting to look at this from a personal perspective and this is a team game, so you can’t exactly do that.
You don’t need a majority of games to have throwers, smurfs, or cheaters. You only need some of them to. I have a 50%+ win ratio on my mains (see: Reinhardt, D.Va, Orisa, Winston, etc.), yet I still wasn’t able to reach diamond this season. Why? Mainly because of throwers, useless DPS, or some other reason. I often found myself in situations where I’d get one or two good teams, then I’d get queued up with bad players for the next three or four matches, completely undoing any kind of progress I made.
Now, that doesn’t happen all the time, as you said, but it happens enough to make a difference, especially since SR isn’t distributed at a flat rate until reaching diamond anyway, which you also failed to mention. In any case, you’re only fooling yourself here if you honestly believe you’re the only reason why you managed to climb from silver to diamond. You’re also fooling yourself if you have convinced yourself that you’re the only reason you can’t climb any higher.
There’s a lot more going on in this picture than you seem to be aware of.