Love the question and the entries!
First, I have to say that some of the comments already posted are stretching the term “virtuoso” IMO. If you set the highest human achievement at a 10, say Steve Morse on guitar, or Dave Weckl on drums, then you have to say musicians like John, Paul, George and Ringo fall somewhere around a 5.
But I’m not here to be contentious…
There was a line up of musicians that produced the best live concert I have ever seen
The live album was called “Bursting Out.”
Ian Anderson: vocals, flute, guitar, concert crash cymbals
And because of a flute solo only he could produce I’ll give him a 9
Martin Barre: Various guitars, mandolin, marimba =8.5
John Glascock: Bass, Guitar = 8
John Evan: Piano, Organ Synth, Accordian = 8
David Palmer: Pipe organ, synth, and most importantly, arrangements = 8
Barrie Barlow: Drums, glockenspiel = 9
Band = 8.33
If I could give the creativity of the actual music and lyrics a rating it would be a 9
Another band to consider is the ensemble that Sting first put together when he left The Police. (And they weren’t bad neither)
Sting: Vocals, guitar, doublebass, synth. (His mastery of instruments is competent, but I give him a number primarily for his vocals) =9.5
Omar Hakim: Drums =9.5
Darryl Jones: Bass = 9.5
Kenny Kirkland: Keys = 9.5
Branford Marsalis: Saxophones = 9.5
and excellent female back up vocals
Band Total = 9.5
Of course one could say that they weren’t really a band, but Sting has had virtuoso musicians tour with him for years that are close to being considered band mates