So I have played everywhere from bronze 4 to gold 4 over the years. I was never challenged in lane (except somewhat by regular jungle camp of my lane - just to help their laner go EVEN with me) until about s1/g5. Yet here I sit this season in s5. I didn't suddenly lose all my skills that got me to g5. And there aren't 400,000 new players who joined that are better than me since last season.
I agree in the VAST MAJORITY of cases, people are where they deserve to be. However after this season, I can attest that it is not always true. For example about 2 months ago, I had climbed to s3 and was set for promos. Then get a 2 WEEK losing streak where I have about 90% of games as auto-losses (0 chance to influence map or carry). Well if I'm 1v2 camped by enemy jungler and team refuses to gank for me ever, going even for 15 min or even pulling off a 3/0/0 start is more than doing my part. Yet even when I pull off a 3/0/0 start in a 1v2 lane where the enemy will flash gank at every opportunity and gank when they have no flash too, I end up getting into an early/mid game teamfight and deleted by 5 hits from a 12/0/3 enemy adc or 1-shot by enemy mid DESPITE building appropriate tank items as quickly as possible. Meanwhile my team has fed so hard that 4 of them can't deal with a 0/3/0 enemy that I solo destroyed in lane. When you get 2 straight weeks where no joke 90% of your games are like that, there is no carrying. Type anything to teammates and they at best just ignore you; 98% of time, they flame and throw harder. So keep your beliefs all you like, but there are exceptions.