Agree @stuartk. It just occurred to me that another element to remember is that The Band are actually from a generation before Petty and his guys---The Band of the 50’s, Petty of the 60’s. That was one reason Petty seemed out of place to me in The Travelling Wilburys; Tom seemed like a kid in a group of adults.
By the time of Petty’s debut, I had already followed the musical path back to the origins of what lead to Rock ’n’ Roll: The Carter Family in Hillbilly---onward to Hank Williams and the other late-40’s/early-50’s Hillbilly singers (including Lefty Frizzell, whose "Long Black Veil" The Band included on Music From Big Pink), and the Jump Blues of the 40’s and early-50’s (Joe Turner, Louis Jordan, Big Jay McNeely), from which Elvis "borrowed" much of his early sound and style.
And you’re right---The Band’s music reveals all those influences, and more. Petty & THB sound like they had heard nothing before The British Invasion---very shallow roots. I don’t know what it was like in Florida (Petty’s stomping grounds), but in the Bay Area (mine), Roots music was what all serious musicians were diving into.
Jerry Garcia was playing Bluegrass in Palo Alto (just a few miles north on the El Camino Real from my hometown of Cupertino) before forming a Rock band, his future-buddy David Grisman doing the same in Mill Valley (across the bay from San Francisco). In the early-70’s we had Dan Hicks & His Hot Licks, Commander Cody & His Lost Planet Airmen, Asleep At The Wheel, The Electric Flag (with Mike Bloomfield), Charlie Musselwhite (with the great Robben Ford on guitar. He later worked with Joni Mitchell, Miles Davis, and George Harrison, and was in The Yellowjackets. Damn!), Maria Muldaur, and so many more superior artists.
After hearing all them live in clubs and on record (plus all the bands and artists Bill Graham brought into The Fillmore Auditorium and Winterland---Albert King and other such masters), Petty seemed like a light-weight! Yet, to me, Twilley doesn’t. He has a distinct-1950’s influence evident in his music that is absent in Petty’s. Perhaps it’s just that I’m more fond of 50’s music, Petty of 60’s.