My educated guess is that when Charley T. “Muddy” Wilbury Jr. assembled his Heartbreakers in Gainesville, Florida, he never thought they’d be as influential as many of the artists that inspired them.
Founding and current Heartbreaker bassist Ron Blair (1976-82, 2002 – present) and his intermediary, the late Howie Epstein (1982-2002) excelled in their supportive roles.
Blair was a bit more adventurous in the pocket as evidenced on Damn the Torpedoes (1979), Mojo (2010), and Hypnotic Eye (2014) wherein his harmonic movement and occasional embellishments surfaced amid the more sonically audible din of his mates.
Epstein, who was also an accomplished vocalist, additionally distinguished himself as a producer on John Prine’s extraordinary Lost Dogs and Mixed Blessings (1995), and Eric Anderson’s Grammy winning Memory of the Future (1998), among others.
Studio legend Duck Dunn played on two Petty tracks from the band’s first and third releases respectively – however to my ears, Donald did not render anything Mr. Blair couldn’t have cut.
As a bassist and vocalist for Mudcrutch (1970-75, 2007) and the Traveling Wilburys (1988-90), Tom Petty hardly deviated from the root -fifth routine on every track, which is exactly how you’re supposed to behave in the presence of Bob Dylan, George Harrison, and Roy Orbison en masse!