People who say this game isn't luck based are living a lie
If your midlaner decides to first time bloody Aurelion Sol in ranked and feeds fizz with 10 kills in 15 mins then whatchu gonna do
If your toplaner decides to ragequit and never come back at minute 8 whatchu gonna do
If you get a troll in your support who runs it down and has a score of 12 deaths in minute 20 whatchu gonna do
And its the same the other way around. Enemy has a troll or two? Good job, free LP. The remake bugs and you are 5v4 from the start? Good job, free LP. Enemy picks Azir first time against a million mastery point Leblanc? Good job, free LP.
You can't say this game is not luck based. Team A might play with all their mains while team B got unlucky and 3 of their players main champs were banned or already picked.
I can go on for hours to tell reasons why this game has not much to do with skill. At least not in the lower elos.
Of course you can contribute some to the game. For example I am support main. I ward my ass off, but if people dont look at the map then what can I do? I ping and warn people when I see the jungler enemy about to gank but if they ignore it what can I do? I can ping drake when 3 enemies are dead but if no one cares about objectives and rather wants to farm what can I do?