First things first: i was talking about hard rock numbers, prompted by the "whoa mama" comments of gibsonfan. Percy has of course written his fair share of beautiful/smart/evocative etc. lyrics, but my point was: although on first glance the hard rock songs of the Stones and Zep may seem to be of equal lyrical quality, closer inspection reveals that the former had a way better knack for rocking out AND having words that most of the time (not always, of course) go far beyond the cock rock cliches Plant wrote.
Second, I'm sorry, but Thank You has really banal lyrics for my taste, but to each his own, I guess.
Finally, "all far more evocative tunes"? Really? Gimme Shelter, You Can't Always Get, Wild Horses, Dead Flowers, Moonlight Mile, Sister Morphine, Sympathy, No Expectations, Paint It Black, Shine A Light, Winter, 100 Years Ago, Waiting On A Friend are only some of the songs in their discography that display an astonishing marriage between music and lyrics. But I guess the thunderous terror of Shelter, the spiritual uplift of YCAGWYW, or the spooky, creepy "dark alleway" vibes of Sister Morphine are less evocative than what Zep had to offer...
And don't make the mistake of dismissing their post-73 output...the "they sucked after that" myth is exactly that...a myth.