Your picks of mediocre or lousy vocals with great musicians!

Ringo

Most vocalists are mediocre pretty much by definition compared to the best.

Many mediocre, and even technically poor vocalists still have the "it" factor to be a "star" and over the years typically get set up with the the most talented musicians available to make a good product.

Bob Dylan demonstrates one need not be even a mediocre vocalist technically or even be overly physically attractive to connect and be a star. I would rather hear Dylan sing any tune he is committed to than than most very good vocalists who may just be going through the motions.

The example of a mediocre vocalist catapulted to stardom that comes to mind is Mick Jagger. I love the Stones but much prefer most studio versions of their stuff to most any live performance mostly due to Mick’s mangling of the vocals in comparison. Just me.

Jim Morrison? Wait a minute! Aren't rock vocalist SUPPOSED to be lousy?

Mapman,
Mick Jagger isn’t mediocre vocalist. He’s lousy and always off the key.
Not attracted neither to Bob nor Mick, but would love to hear Dylan’s songs performed by great jazz vocalists rather than Dylan sing himself. Not his job IMHO.
Just me or maybe not.
Dweller,
Yes. The rock vocalist MUST be lousy to the point of goose bumps on skin sounding similar to opening of the old rusted shed door or grinding noise of breaks with worn pads! Axle Rose I guess is champion.
Can’t tell that about Jim Morrison, Peter Gabriel or even David Byrne.

The Byrds did wonderful versions of Dylan songs. 

Can't think of any other Dylan covers I enjoy as much as Dylan's.

Dylan's is a case of an effective voice.   Not good at all rally technically.  He's also not a great musician either some in the know say.  For all it matters.