You can Vote for Most Valuable Lead Vocals (Rock Groups)

Hi, map.
Morrissey was the lead singer of The Smiths.
The Smiths simply would not be The Smiths without Morrissey, no substitute.
No Morrissey, no Smiths.
He also wrote or co wrote their songs. 
Unique voice, unique lyrics, unique sound.

It’s true lead singers are key to a group’s success.

The MVP though plays a key role in elevating that group above others in other words the value can be measured by overall success. So a guy like Mick Jagger would qualify in that they are a very successful band. What if the singer was not Mick? Mick is not a great singer. Would the stones have been better off with a better singer? Probably not because Mick also played a major role on writing their songs. So an MVP despite not being a great technical singer. In fact I often think the Stones would be better served live with a better singer because Mick’s live performances though entertaining have often been very ragged and inconsistent vocally IMHO.

Nobody is mentioning the women.
What was Steeleye Span without Maddy Prior?
Fairport Convention without Sandy Denny?
The Pretenders without Chrissie Hynde?
Quarterflash without Rindy Ross?

This being a (de facto) male-only nerd forum, I suggest we remember how many riddles are solved by simply imagining that the hypothetical "doctor" is a woman. 

Annie Haslam made Renaissance successful. 

Ian Gillan of Deep Purple