Look, Zep were basically a blues rock band. I get that you don't like them that much if you're looking from a metal listener perspective, but you can't take away their influence on hard rock.
They were the first supergroup, and one of the best musicians around. Bonham's drumming was one of the heaviest and the time. And they also have a lot great songs - Heartbreaker, What Is And What Should Never Be, Out on the Tiles, Black Dog, When The Levee Breaks etc.
I don't like them as much as I used to and I may say that I like DP more, but both bands were great at what they were doing, both were innovative and comparing which is better seems a bit pointless to me, everyone should just pick the one they like more.
Maybe you might check out Presence, it's probably their heaviest album and Plant's voice is a bit lower than before.