With all due respect (I can’t help but think I’m sounding like Cliff Clavin here..lol), the book “Hammer of the Gods” description of John Paul Jones pretty much nails him as the real brains of the band. The only one coming out of the whole thing toward the end of their run with any real money in the bank, he was responsible for a great many of their signature riffs and a master of arrangement at age 18 working in the studio in Liverpool, doing just that at the time for top name bands. Unheard of in the day at that age. On tour, he would lock himself in his hotel rooms and while the others were partying and doing heroin, he was writing and taking care of the music. That is not to take away from the writings of music by Page (also his studio abilities) and the lyrics of Plant at all, though. They just let the rock and roll life distract them, as young guys will. Well, that really was a bit long winded...sorry for that.
But for me the proof was the post-heyday work. Plant's compositional genius really shone since Led Zeplin. His best work, IMHO, and as good as any pop composer's, better than most.