Top Ten Rock Vocalists

ghosthouse, the artists you just mentioned definitely are not hard rock/metal or prog.! But I think at least some of their music could be considered Rock.😎

This list mentions a lot of the usual suspects. If you want to focus on rock, it is worth mentioning the Seattle crowd:
Chris Cornell- Soundgarden
Eddie Vedder- Pearl Jam
Layne Staley- Alice in Chains
Mark Lanegan- Screaming Trees

I particularly enjoy Lanegan's whiskey soaked baritone on his solo albums.

Arcam - I think you put your finger on what was jamming me up...the difference between a characteristic style and belting out the occasional rocker.

maxnewid, Chris Cornell is on nutty's 'list and also on my list. Great singer!😎
I have never been a huge Eddie Vedder fan but that is a matter of personal taste and that's cool.
Layne Stanley is a good choice, very unique voice.
As for Mark Lanegan I am not familiar with the Screaming Trees but I will look into them.

On my unwanted rock vocal list
Steve Tyler and Axl Rose leading followed by Bruce Springsteen. I won't stand even few min listening to those...