What does 'greatest' even mean in this context? Commercial successfulness? Influence on future bands? How good their music is (which would of course be 100% subjective opinion)?

It's a pretty loose term.

It's not a superlative I would use when describing LZ but I can understand getting really swept up in their music.

Well if Buzzfeed says something, it must be true.

Years back VH1 were into polling a bunch of musicians (200 total) across a wide range of genres to compile various 'best of' lists.

Greatest Artists
1. The Beatles
2. Michael Jackson
3. Led Zeppelin
4. The Rolling Stones
5. Bob Dylan
6. Jimi Hendrix
7. Prince
8. Elvis Presley
9. James Brown
10. Stevie Wonder

Greatest Hard Rock Artists
1. Led Zeppelin
2. Black Sabbath
3. Jimi Hendrix
4. AC/DC
5. Metallica
6. Nirvana
7. Van Halen
8. The Who
9. Guns N Roses
10. Kiss

Well if 200 musicians say something, it must be true.

Lol that's one of my favourite articles. Half of the items are basically "Led Zeppelin is the greatest because they're famous and rich as ****."

How ****ty were the artists they talked to?

The credibility of the whole thing is called into question by Kiss being on one of the lists. Plus, if you ask any large group of people the same question, the common denominators are going to be a bunch of famous artists.

Have you ever been to a KISS concert?

Thank god no.