That's a pretty negative mindset you've got there.
Look, there are a lot of things in this game that make for easy scapegoats when sh&$ hits the fan and you end up losing. And even though I disagree with you, I'd be insane to say you are wrong. Yeah it's possible to do everything right and still lose, BUT that doesn't mean that this is a game of luck.
I'm reminded of a quote who's origin I forgot, "You don't need to always carry, but just be light enough to be carried." Self improvement is my point. In every game, wins or loses, try to find your faults and mistakes.
For example, myself. I've been in low silver the past two seasons and as of this post I am b1. I can confidently say that my knowledge of the game is solid enough that I am par with low gold, but my fingers are not up to speed. My reaction time and precision is awful. I often don't click fast enough or on the things I want to click often enough. Knowing how to freeze lane, when to roam, or what a comp needs can only do so much if you can get out speed by a comatose dog. As a result, my better games tend to be when I'm the weakest player on the team as I know enough to avoid dying consistently, but when I'm the strongest of the team I can't carry. This is why I've been stuck in b1-s4 area.