Your performance IS MOSTLY irrelevant.
I'm a Teemo MID main who buys support items and I'm Plat IV currently, been working towards diamond since end of last season, I'll get there. However, I say that to make the point that while I'm a freaking amazing Teemo, Teemo mid is not good, it's always a brutal fight. If I was super super serious I'd play something different. Rather, I enjoy the challenge of taking on off pick to high tier and out performing the best 10% of the player base, it makes me laugh. That said, the only reason I can get away with this is that even if I lose lane my chances of winning are STILL near 50% on any random lane loss game pick you look at. This is because your individual performance is not irrelevant, but is mostly irrelevant.
Reasons your performance matters:
- You can snowball the 'winning' mentality of your team if you do well. If you do well it's easy to encourage others to do well. If you do poorly that tends to be reflected in your teams attitude. I would argue that champions and skill level of your team is maybe 30% (somewhere in there, I realize it seems like an arbitrary percentage) of your capacity to win. The majority of your capacity to win any given game is your teams ability to work together and function as respectful and aware of each other. If you can't do this you probably lost, hence why solo q is mostly a sh*t show because you never know what random A$$hole is going to be on your team.
Outside of this your perfromance mostly doens't matter. You could practically AFK and still win 30-40% of your games assuming your team still tried to win. If all you did was ward the jungle all game you'd still win 40-50% of your games. Bold claim? I challenge you to seriously reflect on this. What makes you win >50% of your games is you doing well consistently across hundreds of games. This doens't mean that any one game you do well on will automatically be a win, just that it is statistically SLIGHTLY more likely to be a win. Lets put it at 55-60% likely to be a win, that may be generous. When you spread a consistent favoring win average across hundreds of games you climb the ranked ladder.
Conclusion:
Your one anecdotal game example of you doing well and losing is statistically irrelevant.