Which is why Peter Grant assaulted Grand Funk Railroad’s manager, threatening him if they didn’t pull out as Zep’s opening act, because they were blowing Zep off the stage.
As a trio, GFR were right up there with Jimi Hendrix or Cream. Once they added keyboards, something changed.
BTW, Vanilla Fudge insisted on putting Zep on their 1969 tour, and even agreed that whichever band had the #1 song in whatever city they were playing, that band would headline.