You can’t win every single game, unless you’re a T500 in bronze. Even then, even a T500 will lose if all 5 of his teammates leave the game.
But as for ranking up, countless players have shown that you can consistently maintain >50% winrates and gain SR if you play better than your rank. This has been shown time and time again, both by smurfs (who cause plenty of problems) and by legitimate players who just got better.
My personal example - I was hard stuck in plat for several seasons. I got a new graphics card (up from integrated graphics) which had a huge impact on my performance, and I immediately climbed to mid-masters with a ~65% winrate. This was on Rein-Mercy back before 2-2-2.