Your picks of mediocre or lousy vocals with great musicians!

Yup Marty, I do buy your point. Mozart is the master of the piano concerto and sonata. I actually prefer harpsichord to piano though, and am very grateful for the "authenticity" movement that brought back the instrument. Such sophistication and dignity!

It seems to me that those posting here come with differing points of view:
(1) Musicians
(2) Hobbyists
(3)Those in-between
I respect those views. EX: If I, as a hobbyist, say an artist is great, a musician will most likely say that artist is "skilled". This is a point of contention here, I believe.
I believe I was put off initially by the OP's title. "Lousy vocals". This really got under my skin.
The reason it got under my skin was, the very thought of saying "lousy vocal" implies that one has NO appreciation for artists that aren't tonally correct and/or have less than optimal vocal range/ability.
This term "lousy", should have been the subject of one poster's response..."panties in a bunch".. IMO. A more appropriate term could have been, "less than stellar"? Get my drift? This would have been more acceptable to all and much less offensive to everyone!
The preface for this thread was (wrong) in it's wording by all accounts. It doesn't take into consideration the passion an artist has that can transcend spotty vocals and can make their song better than another, that may have perfect vocals. 

...I do believe, when all of the dust settles, we have handled this much better than our current politicians have handled their debates! This is suppose to be a humorous gesture. Cheers!

Bob Dylan
.mediocre voice? yes
.mediocre musician? yes
.not enough superlatives to describe his music? absolutely YES

All of my favorites are flawed (Garcia, Dylan, Young, etc.) but absolutely remarkable. I don't have the stomach for "american idol" type musicians. I'll take emotion and character any day over smooth and predictable.