To an extent.
Once you learn the games core mechanics, you should basically be able to perform at gold+ level. CSing, positioning, team fighting, map awareness, vision, lane manipulation, how well you know your champ, its counters, what it counters etc, then how you execute all of that together i would say is the core of the game. Once you learn all that and a few things i left out because I'm lazy, i feel you should be able to perform at least at a gold+ level.
But after that i feel it's quite luck based. Whiny feeders throwing a tantrum and taking it out on the team, 3 autofills, a dc, or a lagger, or someone using a fucking potato to play the game getting 10 FPS in team fights come to mind as shit out of your control, that directly effects the outcome of a match. Match making in general is a nightmare, and completely coin flip. (queue the hate for saying coin flip)
I mean most people at Gold+ just use OP.GG or some shit, and check autofills/champ winrates and dodge accordingly to climb. That kind of really shows a flawed ranked system that really does depend on a lot of factors that are completely out of your control.
But yeah if you are stuck in iron or bronze or some shit, that's probably due to lack of core game mechanic knowledge. Since most of those elos you can pick a hyper carry and just 1v9. But once you get to where mostly everyone if not everyone knows at least semi what they are doing, theeeeeen it kinda relies a lot on how well your team performs.
I'm sure we have ALL been there, where 5 minutes into the match, your bot lane is already somehow 0-6, and the fed ass enemy bot has arrived to take YOUR lane before you even had a chance to do jack shit. I'm sure there are idiots out there who will go "winnable" at that point, but we all know 9 times out of fucking 10 that is a loss, and you will have no impact purely because of how hard the enemy is snowballing. Kinda hard to have an impact when one right click does half your life of HP.
So yeah, to an extent. But once you get to id'e dare say gold/plat/diamond and up, then it's more coinflip and luck based than anything.