Of course people with many games will have a winrate closer to 50%, that's the point. The more matches you play the more accurate of a display of your skill it is.

That isn't to say that a lot of the top players aren't good (because most of them are!) but using Aether as an example, most of the top 10 last season were hovering around 53 - 55% winrate after hundreds of matches, with only one outlier. So now they know better than to spam games out, because all it can do is harm them. It's a shitty system that incentives getting a good spot early and then just stopping because playing more puts you at risk.