"The Night They Drove Old Dixie Down".

No joke at all.  Garth would provide instrumental texture and density to the LZ palette.  It's a role that JPJ did for them in the studio.  The original Jimmy Page concept for LZ was as a twin guitar band with Terry Reid as the vocalist, co-lead guitarist.  RR can't sing, but he rock a Strat or Les Paul with the best of them.  As an added bonus, LZ's lyrics would have been upgraded.

@onhwy61 ”John Bonham couldn’t play in The Band. No way.”  
“No way”??? How is this statement logical?  
Levon could be his typically great self, singing wonderful lead vocals, singing great backup harmony vocals, and playing a multitude of instruments.
The musical difference in the songs of The Band and songs like “Tangerine,” “Hey, Hey, What Can I Do,” “Boogie With Stu,” “Bron-Y-Aur Stomp,” “Your Time is Gonna Come,” “Black Country Woman,” “That’s the Way,” “Gallows Pole,” and “Down By the Seaside,” is minimal.  
Furthermore, each of those songs feature extremely sensitive, tasteful percussion that serves only to improve the song.  
John was an extremely sensitive and intuitive artist who simply loved music; simply loved good songs. Bludgeoning the skins was not imperative to him. It was just another thing he did. In the case of Led Zeppelin, it came in handy.  
Again, this was not imperative to John’s artistic expression, just another component that may or may not be useful depending on the song.

“Plant, it’s a few decades early in his development.”  
Come again?  
Plant is a perfect contemporary of The Band (‘68-‘76). If that is true, and his vocals were, at best, equally good (at worst, demonstrably worse) in advanced age, how can your statement on Plant’s “development” make any sense?

I know John Bonham only from my very limited exposure to his playing on Led Zeppelin albums. I heard their debut when it came out, and found it unintentionally and almost hysterically funny, like the bar band in the movie Ghost World: Blues Hammer. The name is quite apropos, as that fake-Blues band heavy-handedly bludgeons the music to death, employing no restraint or subtlety what-so-ever. As did, imo, Led Zeppelin. And in anticipation of the possible reaction to this statement by some readers: no, I am not saying this thinking it makes me sound cool (or whatever).

But by the time Led Zeppelin I came out, I was already listening to the Blues Levon Helm had grown up listening to and then playing in The Hawks, that of it’s originators: Muddy Waters, Howlin’ Wolf, Big Joe Turner, Little Walter, Sonny Boy Williamson, Robert Johnson, Freddie and Albert King, Slim Harpo, Roy Brown, Wynonie Harris, Jimmy Reed, etc. As well as the American bands that had been putting out albums of Chicago-style Blues for several years before LZ showed up: The Paul Butterfield Blues Band---whose black rhythm section Paul hired away from Howlin’ Wolf---and Charlie Musselwhite primarily.

That may not be enough to determine if Bonham could have played in The Band, but imo his bass drum technique alone would have disqualified him. Like many Rock drummers, Bonham "buried the beater." That’s what drummers call punching the felt beater of the bass drum pedal into the batter head and leaving it there, rather than letting the beater rebound off the head, which is called "feathering." Burying the beater causes the forward momentum of the music to stop and start on every down beat (the 1 and 3 in 4/4 time). I can’t get past that in the music of LZ.

Levon Helm employed feathering (as do jazz drummers), and other subtle aspects of the approach to playing the drumset (Buddy Rich "approved" of Levon’s playing 😉). Bonham may have had his strengths, but subtlety was not amongst them. Levon was also very sparing and selective in his use of the crash cymbal, a rarity in Rock music. Most Rock drummers tend to crash at the end of every measure (4 beats in 4/4 time), for no musical reason. Such cymbal crashes chop the music into separate little sections, rather than one forward-moving train. Bonham was very guilty of that musical "crime". He didn’t know which notes to leave out, overplaying---again, very common amongst the drummers in Rock bands. The Band were not a Rock band, they were a Rock ’n’ Roll band.

To hear how "sluggish" Bohham’s drumming is, listen to his opening in the LZ song "Rock ’n’ Roll", and compare it to the "crisp" drumming of Earl Palmer on Little Richard’s "Keep A-Knockin’", which is from where Bonham "borrowed" his part.

@bdp24 those songs I mentioned beg to differ.
The Band was nowhere near the aggressive musical outfit that Zep was.
Zep often played big ol’ aggressive music wherein the bludgeoning you referred to was not only appropriate but beneficial.
Given the technical proficiency, versatility, sensitivity, and tastefulness of Bonham’s drumming (the 3rd-through-8th LPs are the ones to listen to, I’d personally recommend III and Physical Graffiti, NOT the derivative, Blues Hammer 🤣 first two LPs - I love that reference, BTW 😆), it’s exceedingly difficult for me to believe he wouldn’t have brought all his creativity and subtlety to those Band songs, and/or been more than willing to “tone it down a notch” if one (or several) of the guys asked him to 😉.

One reason I cut Rock band drummers some slack---especially those at the level of Led Zeppelin---is that they are playing in very large venues, and the music has to reach all the way to the back seats. Playing "lightly" and with subtlety just doesn’t work in that scenario---it gets "lost".

There are two Rock bands whose drummers I like a lot (as well as the band’s music): AC/DC and Weezer. And wouldn’t ya know it, they are both more Rock ’n’ Roll bands that Rock ones.

One trait of Levon’s playing that I know without a doubt was beyond the understanding of Bonham is perfectly displayed in what Levon plays as his entrance into "The Weight". Robertson plays his acoustic guitar intro, after which Levon hits his floor tom on "1", rests on "2", hits his tom again on "3" and "4", then comes in on full kit on "1" of the first verse. Brilliant!

The thing is, ANY drummer can play that simple part, but no one else ever has! It sounds SO cool, and so musical. Most drummers would play something difficult to execute, to show off their chops. That would be done not in service to the song, but to their ego and pride.