I might say 60% skill and 40% luck in ranked specifically, and if you are above gold I would say closer to 70/30
Even at the highest level you still have to factor in:
- the unlucky afk,
- the enemy team ending up with the more skilled on their champion players vs
- your team "trying x champ out" in ranked, because people do that for some reason
- someone having a bad day and raging, or being on tilt from losses, etc
- the jackass who trolls because...who knows why people do that in ranked
The things above aren't guaranteed to happen, but when they happen, it can make winning that much harder, and pull the control a little bit out of your hands, but not completely.
I wouldn't say any match is 90% skill vs luck or 90% luck vs skill, but luck IS a factor. Skill is just a more important factor.