One of the RSS videos estimates that you teach about 30 different ways of creating, distortion.
This, along with all the other choices in rock vocals gives someone a wide variety of choices to choose from when building that tone and character of the voice they want.
Someone whose biggest influences are Ronnie James Dio and Geoff Tate are likely going to make very different choices in what techniques they choose to excel at then someone whose two major influences are Robert Plant and David Coverdale.
Someone whose biggest influences are all nu metal vocalists will make yet different choices.
It would seem to me that vocalists tend to learn maybe just 2 or 3 types of distortion and really try to master them, rather than trying to get good at many distortion techniques.
Just using Ronnie James Dio as an example because of how highly regarded he was by both his fans and his peers, if you were to identify how many of the different techniques for distortion he used throughout his career in Rainbow, Black Sabbath and Dio, would you expect to find more than two or three techniques he employed?
I would guess not, but I'd like to know your opinion. My idea is based on Bruce Lee's philosophy that dictated: "I don't fear the man who has practiced a thousand different kicks. I fear the man who has practiced one kick a thousand times."