Songs about other singers: C/D

Jimmy Webb - "P.F. Sloan"

I was going to mention that one but that's really about him as a songwriter.

Madness, "Prince Buster"

Yeah I was on the fence about "P.F. Sloan" but he literally says "listen to him singing" so I'd count it. Prefab Sprout's "The Songs of Danny Galway" (about Webb) seems to be just about the songs tho

Sparks "Lighten Up, Morrissey"
Warlock Pinchers "Morrissey Rides a Cockhorse"

also not extolling the greatness:
Mr Floppy “100,000 Morrisseys”

Sparks also have “Edith Piaf (Said It Better Than Me),” and “When Do I Get To Sing ‘My Way’?” in which the singer aspires to the heights of Frank Sinatra, or failing that, Sid Vicious.

Makes me wonder whether songs earnestly praising other singers were a common trope in 30s/40s Calypso music

Sinatra also praised in the Calypso record “Bobby Sox Idol” by Wilmoth Houdini, sampled by The Avalanches on “Frankie Sinatra,” with lightly Sinatra-referencing lyrics by Danny Brown.

The Knife - You Take My Breath Away is mutual lovein by/about Karin + Jenny Wilson

"I'm in the first row on your show, in the first row
On the First Floor Power show
Your vibrato's like vulnerable leaves
You do it crazy, that's how you talk to me"

"I heard you for the first time on the radio
When I was going somewhere in a car
You touched my heart, like a knife that's very sharp"

The Mountain Goats have lots about artists in other nonmusical media but some fitting this thread include:
"Song for Dennis Brown"
"Andrew Eldritch is Moving Back to Leeds"
"Abandoned Flesh" (Gene Loves Jezebel)
"Waylon Jennings Live!"

It's not about a singer or by a singer but my favorite musical elegy song is "Goodbye Pork Pie Hat" by Charles Mingus about Lester Young. I know I've heard versions with lyrics that someone wrote to it, can't remember who.

The band Helen Love has multiple songs about Joey Ramone, and the song “Debbie Loves Joey” adds Deborah Harry as a metaphor for glamour and excitement felt by teenage lovers.

Another act used as a relationship metaphor: “We’re The Pet Shop Boys” by My Robot Friend.

(also covered by the Pet Shop Boys live, as a B-side, and backing Robbie Williams.)

(love Helen Love)

Dylan:

"Song to Woody Guthrie" (also "Last Thoughts on Woody Guthrie")
"Blind Willie McTell"
"High Water (For Charlie Patton)"
"Roll On John" (Lennon)
"Mr. Tambourine Man" (Bruce Langhorne)