Sampson , we at the vocal thread decided to give 50 % of the importance to influence/impact when making a 'greatest' list, do you agree with that ?? If so , then I would ask the placement of Stevie Wonder , cause I would assume him to be much higher than he is....
Umm, he might jump three or maybe four spots on my list here if it was 50%, but he wouldn't get higher than that, the guys in the Top Ten all have him beat in those areas. If you actually do give half value for that, McPhatter knocks Jackie out of the top spot. Hands down the most influential vocalist in rock history, he basically set the standard for the way all singers approach rock songs. All of the improvising and personal flourishes that exist outside of what's written stemmed from him "taking liberties with the melody". That was bizarre in 1950 where vocalists followed what was written, but ever since then it's hard to think of a singers who wouldn't deviate from what's on the page and inject their own style on a song. He basically showed how to deconstruct a song and then rebuild it by your own design. Jackie himself was actually TAUGHT to do this by Clyde when both were in the Dominoes briefly before McPhatter left to form the Drifters and Jackie took his place.
So be sure when you are settling on the criteria you know what it will reflect. Influence in vocals is very hard to come by but there are a handful, McPhatter, Hamilton, Plant, who have SO much that it will elevate them enormously.