Sigh. This is somewhat of a rant not directly targeted at this thread or anyone in it per-say.
Part of the problem when you're talking about Cliff is all the fanbois who are like: "ZOMG HE'S TEH BEST EVAR! LISTEN TO MOP OMG OMG OMG!!" Then pretentious Jaco or Manring fans say: "Oh ya? Listen to this (insert youtube link here). Then tell me he's better". Or people bring up other bass players who're known more for their solo work, or studio work with zillions of other bands across different backgrounds and this and that and that and this. What everyone who does that loses sight of is the fact that none of those bassists they mention, while good, were in Metallica, or were a part of the metal movement that arose at that time in LA and SF. Being a lead bass player, like some one like manrig or Jaco or anyone else like them, in a 2 guitar 80s thrash metal band is about as easy as stopping an avalanche with a set of snow shoes. When you enter into a situation like that you've got to do what works within the confines of the band.
People also lose sight I think of the fact that Cliff was only 21 when he put out his first album (Kill em all), and only 24 when he died. Jaco was 23 when he put out his first album, and died when he was 35. Sean (Malone), and Manring likewise were both older than Cliff when they released their first albums. So for some one who was touring the world by the time he was 22-23, and really only starting to explore his possibilities as a bass player, I don't think it's really all that far off the mark to assume and rank him on what he "could" have done, not to mention that in my opinion it's an unfair comparison to some of the true greats of solo virtuosic bass playing, because, quite simply, Cliff wasn't a solo player.