CCR do not fit the criteria for a "supergroup" to me.
I'm talking about groups where each member was already a superstar in their own right before the group. The Fogertys had big solo careers AFTER CCR.
I suppose Derek & the Dominoes, and Blind Faith do fit the bill, but I still think those 2 groups (Traveling Wilburys and Highwaymen) are in a whole different class. I mean come on, are there bigger names then Bob Dylan, Roy Orbison, George Harrison, Johnny Cash, Willie Nelson etc..
And the Wilbury who's always forgotten, Jeff Lynne, I believe is one of the most underrated singer/songwriters of his time. Same goes for Kris Kristofferson of the Highwaymen.
Still can't decide which is greater.