So, we work with these guys and I can tell you that right now this is definitely low in terms of an estimate of the money they are making.
In addition to what they make from ads, a lot of YouTubers will get paid to make videos that involve a product, etc. For some (most?) that is actually a larger source of income than the AdSense.
Also there are many many more than 10 YouTubers who are doing very well from their channel.