Uwe, with all due respect, your knowledge of Metallica is more than a little fuzzy and not just for equating Cliff Williams to Cliff Burton. While I agree wholeheartedly that had Cliff not died, there would have been no "black" album (how I wish!), he was very much the key ingredient to Metallica's early success and what ultimately led them to superstardom.
Before they left LA, Metallica was just another Sunset Strip thrash band whose only noteriety was Dave Mustaine's songwriting. When they moved to SF so that Cliff would join, their sound changed completely. Cliff was the only theory-trained musician in the band and he taught Hetfield about song structure and dynamics. His love for Thin Lizzy's dual lead harmony gave Metallica a melodic lift beyond the simple chugging Euro-thrash that Lars and James were aping prior to his inclusion.
He has never been given his due as a respected technical player by musical elitists, but that does not mean his abilities began and ended with a Rick bass wah solo. He was very much a victim of Flemming Rasmussen's 70's classic-rock style of production and much of his solid foundation on the bottom was mixed out in favor of a thicker guitar sound. If you want to even hear him appreciably at all, the only record is Kill 'Em All. He's audible there because John Zazula was much more of a promotor than a producer and did not want his new "find" to sound like just another Iron Maiden or Diamondhead. Matter of fact, compared head to head, Metallica's covers of Diamondhead songs highlight exactly the rhythmic difference that Cliff made, because vocals aside, the songs are otherwise very faithful covers; the difference being that Cliff held Metallica to a tight, punchy, crunchy rhythm, while the Euro-thrash was more a free-form meter-stretching plod.
Newstead was in the unfortunate position of being the bass player in his idols' band, and they abused him mercilessly. He did the best he could and did grow somewhat as a player during his tenure, but the fact that Metallica sought out Bob Rock to produce at all already showed their intent to conquer Bon Jovi territory, bass player or not. Their pitiful attempt at musical credibility by replacing Newstead with a bad funk-metal slapper only underscored just how outright LUCKY they had been to have played with Cliff.
