You are right. I'll pass on the invitation, but thank you all the same. But I will say I have one site that does astoundingly well most of the time, and several others that pay me virtually nothing.
How long is a piece of string? What I might call a good site, and what someone else calls a good site differs wildly. Also, earnings vary by so many factors you cannot possibly answer this question.
The only advise that makes sense is to write about something you know about or interests you, promote the site and grow some traffic.