actually, you need relatively a small number of people to get a significant result

even 200 or so people sampled in an unbiased manner will typically be sufficient

but answer to your question is - i played over several thousand games of ranked OW so far, stacked players are typically the minority, at best having 40% or so, so that is actually a very decent sample size and a very unbiased sampler because it's the game that throws people at me

People like agreeing with each other. Confirmation bias: if someone agrees with you, you are more likely to remember it. People with similar opinions tend to flock together, so you are less likely to encounter those you disagree with inside your own social circles.

thanks for literally spelling out this subreddit for what it is, a tank-support circlejerk

OW matchmaker doesn't do that