It doesn't matter. Zep have released 80% of their albms in the 70s, hence they were more influental in that decade.
But not more influential than Stevie Wonder.
How about Zep's songwriting?
Stealing old blues tracks, re-working them and slapping Page's name on the credits? Stunning
According to the revision, he's at #2.
And? According to Rolling Stone, he's #15. I've seen lists with him at #22, #27 [behind the likes of Josh Groban and the lead singer of Tokio Hotel (!!)], #30 (below Ted Nugent, King Diamond and Chuck Billy) and countless others with him far lower that #2.
Yeah, the list on this site was assembled by professional vocalists with lots of expertise and knowledge on the subject who actually researched their stuff, but doesn't mean it's the truth, it's still just a bunch of people saying 'Robert Plant is the 2nd greatest male rock vocalist after Freddie Mercury' (no disrespect meant). There are people who'd laud several others as the 'best singer of all time' before even considering peeps like Freddie and Robert. Doesn't mean anything.