To understand why My Morning Jacket is the most overrated band in modern rock, one had only to hear their attempt to recreate the Band's arrangement of the Marvin Gaye song, "Don't Do It," at the Americanarama Festival at Merriweather Post Pavilion Tuesday. Jim James' blaring, unfocused guitar noodling made him, if not the Anti-Christ, at least the Anti-Robbie Robertson. True, James possesses an astonishing vocal instrument, but so does Mariah Carey, and James' diva-like wailing—mostly vowels and few consonants—made him the Anti-Marvin. And Patrick Hallahan's drumming—simultaneously stiff and cluttered—made him the Anti-Levon.To understand why Jeff Tweedy is the weak link in the Wilco chain, one had only to hear the band's live version of "Dawned on Me" in the set following My Morning Jacket's. It wasn't Tweedy's high-school-poetry lyrics nor his repeating-ad-nauseum, sing-song melody that made the song so appealing. It was the never-predictable sound pouring out of Nels Cline's doublenecked guitar, which helpfully obscured the words and added the missing dramatic tension to the music. And the crackerjack rhythm section of bassist John Stirratt, drummer Glenn Kotche and keyboardists Pat Sansone and Mikael Jorgensen tightened and loosened that tension incompelling fashion.To understand why Bob Dylan's 21st century work is nearly the equal of his 20th century work, one had only to hear his live version of "High Water (For Charley Patton)" during his headlining set on Tuesday. Dressed in a blue jacket with gold buttons, his frizzy, curly hair rising like smoke off his head, Dylan stood at the microphone without an instrument and transformed the 1927 flood of the Mississippi River into a vision of end times. Backed by longtime accompanists Donnie Herron on banjo, Tony Garnier on bass, rhythm guitarist Stu Kimball and drummer George Recife and by guitarist Colin Linden, hired nine days earlier, Dylan sang with a clearer voice and more restraint than in recent years. Having described thunder over Clarksdale, water in the streets of Vicksburg and coffins floating in that water, he sang, "I can't be happy unless you're happy too." Then he paused significantly and in his most serrated rasp, added, "It's bad out there."