I'm all for focusing on yourself and being in control of your own destiny and I think that really holds true in this game. However, I've played long enough to realize that this game doesn't balance me or my opponents, it balances my teammates. If I go on a winning streak playing at a level where I get A's and S's (positive KDA, good awareness and CS, communication, etc.), then I will often go on a streak where I get highly toxic players who troll with picks and/or go AFK. That's not a change in how I play but rather a change in balancing whereby I'm forced onto teams that really have no hope of winning.
Ok, maybe it isn't them, maybe I'm the one on tilt. I'll take a break. If I come back 24-48 hours later, it's the same thing. I don't get out until the 5-10 games pass and I'm back to playing with sane individuals.
This also happens when I duo queue with a friend. It's like clockwork. Last time I played with him, the support thresh decided not to even play because our ADC picked Xayah and "she can't be good on that champ yet so I won't even bother playing."
In reality, the quality of my teammates should stay the same and the thing that changes is the difficulty of my opponents. But that isn't what I've observed.
Riot - Change your MMR algorithm so that it scales my opponents AND teammates until I'm consistently the weakest link on my team. That's where I should plateau at. Not the point where my hostage negotiation skills fail me and my "teammates" decide to blow the team up.