In that it's under produced, under instrumented, minimalist compared to the pop garbage today. Remember that Zep was pop in it's day. I think you have something there.
There is a reason that all the bands who try to sound like Zep wind up failing --they try too hard and over-produce their sound.
Listen to Jimmy's guitars. They are not that distorted nor that loud. Each instrument is just so well produced that it deceives the listener into thinking that there is something there that isn't.
I don't know if I'd call Zep "pop" as I tend to think of 1970s pop as AM radio top-40 which Zep never was. Keep in mind that like the Beatles, Stones and The Who, Zep never won nor was nominated for a grammy -the measure which defined and still defines "pop" music.
I have to hit and run here ..... How many times did Led Zeppelin play "Top of the Pops" BBC show in the UK? For this and other reasons I call them pop. At least they were back then. ....
These days you will hear them on a classic rock station. But back then on pop and rock stations.
Pagey laid 10-20 guitars on some cuts. He double/triple tracked many more. This is minimalist and under instrumented compared to today. No ambient stuff lurking in the back ground for Zep. How many track recorder did they play into? 4? 8? Yup, they are playing folk music. You can contrast this with the Plant/Page remake of "Kashmir" circa 1997. That was a full blown multi instrument extravaganza, which I like in it's own right