Geronimo Black was a group of ex-Mothers of Invention led by Jimmy Carl Black (“The Indian of the Group”). Other members had been part of Love and Dr. John. One album, but not successful.
I may misunderstand your concept, but Mad Season was not made out of the top guys from each band.
We had Layne from Alice in Chains. Vocalist, but less a band-leader than Cantrell.
McCready from Pearl Jam. Again, not sure if he is the “super” part of Pearl Jam.
And a Screaming Trees guy.
A merged group, but not super. Great album they put out, though.
Commercially speaking, Bad Company were a supergroup. But artistically they weren’t.
Free, Mott the Hoople, and king Crimson all were more important than Bad Company.
Not in line with the OP. but to me Tin Machine was an anti-SuperGroup: David Bowie with 3 relatively unknown musicians, with Bowie insisting he was “one of the guys in the band” when the only reason anyone was interested was because David Bowie was in the band. Then there were the Boxmasters, with Billy Bob Thornton on drums, who would get ornery if any interviewer would bring up that he was Billy Bob Thornton the world famous actor, and not just a drummer with the Boxmasters, when in fact the only thing interesting about the Boxmasters was that he was their drummer.
In the 80s and beyond there was Phenomena, which featured several albums featuring mostly peripheral heavy metal artists:
Never been a fan of McCready as a lead guitarist. I am a passing PJ fan - got Ten and maybe one other; listen to their singles. I love the Classic Rock meets Grunge of the song Alive, even though it has been played to death. But man when I hear him kick in with leads at the end it sounds really amateurish.
He is a huge guitar geek - bought a 'burst Les Paul, some 50’s Fenders and Gibsons. I haven’t listened lately but hope he’s kept his chops moving. I get the impression he is a very nice guy and a great bandmate - kinda like Ringo in the Beatles.
Pearl Jam kind of inspired the OP. As soon as they hit it big, they did the two classic douche moves of a new superstar band: hooked up with supermodels and fired their drummer. Dave Abbruzzese hooked up with some bar bands (and worked on some unused tracks for Guns n Roses’ Chinese Democracy). I imagine a group made of fired former members of Pearl Jam, Red Hot Chili Peppers and Skid Row making a go of it somewhere. Some of these sound pretty close.
Does everyone in the supergroup have to have been fired?
David Crosby was fired from the Byrds, but the other members of CSNY left their previous bands of their own accord.
Considering the other two members are guitar legend Joe Satriani and RHCP drummer ( and Will Ferrell doppleganger) Chad Smith, I think you are firmly in supergroup territory there. 