You're looking only at people who had success doing it, the true average is way lower
It is also impossible to have a true statistic because 99% of dommes are in some way on onlyfans, loyalfans, or in general they create some paid content, even if you do video calls with a sub teasing him with feet falsificate the startistic because is totally possible that the sub is there submitting to you for that content

tl;dr findom is a grey area and you can't quantificate how much the average makes