There are 1,809 sets of four Diamond IV+ players in NA and 1.1M total players within the ranked system (NA). That means that, assuming every single player in Diamond IV+ assisted in getting one person into Diamond (assuming you’d need four DIV+ players to raise one person to DV), 1,809 individuals would be boosted. That means that in an absolute worst case, completely unrealistic and insane scenario, 11% of the people within Diamond were boosted.
Taking into consideration factors like not wanting to hurt your own Elo as the booster, having to maintain a smurf to avoid the aforementioned, the chances of anyone Plat or lower having 4 DIV friends, amongst many other things this percentage becomes infinitesimally small. Let’s look at an example simply for some added context: Let’s say that 10% of DIV players decide to boost someone (still an unrealistically high number). That brings us to 724 individuals. Let’s say that 15% (again, being generous) of these players are connected to each other enough that, in a group of four, they would carry someone to Diamond. That leaves us with 109 people. Break that down into groups of four: 27 groups. 27 individuals just got boosted to Diamond. They would make up for .16% of the diamond population. One tenth of one percent. Out of every 100 games you would run into one of these individuals, and half the time they would be on the other team. It’s meaninglessly small and people throw this out there like it’s an actual problem. Someone playing like shit? They are probably having a bad game, or maybe it was a bad matchup, or maybe they are trying out a new champion. And the fact that you’re so focused on their performance tells me that your own skill is just stagnating so you’re venting your frustrations on the poor performance of your teammates.
Sure, this doesn’t account for less serious boosting like getting people into Gold or Plat. Far too many factors to make logical estimations on what’s happening—but I promise you that it’s still small. So small that it’s not worth talking about.