I would argue 70s prog bands and some other hard rock bands (especially the ones that might have straddled the gap between the two, like, say something like a Rush) were just as important. Heck, you could argue early concept albums (e.g., Tommy or Days of Future Passed) are important, too.
But if you are arguing that the really long songs with boring chord progressions they reuse over and over again from song to song and album to album on Physical Graffiti and Presence are the "good" that Led Zeppelin did for the world, then they should have broken up after Houses of the Holy.
I like their early stuff -- like I said, a great blues covers band. I think Houses of the Holy is their best album on a couple of different levels, and I wish they would have kept its more whimsical style.
But the stuff after that... the train kind of goes off the tracks...