Perhaps it is age, but if you really think band members are simply interchangeable parts and it matters not who is in any given band at any given time, then you really just don't understand yet why some bands lineups are considered classic time periods for that band. I could go on forever about how certain periods of a bands existances are better simply because of the members in them and how even one member on bass makes the band what they are. I don't have to go deeper than mentioning Steve Harris of Iron Maiden.
I readily admit that because of your age and the opinions displayed in this thread so far that I don't know if you to even like Iron Maiden or give them their due for the massive influence on almost all the music you probably listen to, but I suspect the majority here can't imagine Iron Maiden without Steve Harris on bass. We unfortunately got to experience them without Bruce on vocals and Adrian on guitar for a few albums that proved quite conclusively they are better with them in the fold.
Metallica was good with Jason on bass - like I said in my post on the 86 show, it was my favorite Metallica show ever and I saw them on 4 of the first 5 tours in support of Ride The Lightning through the Black album. 85, 86, 89, 92 - for my money the 86 and 89 shows were simply better shows, not for historical reasons, just I enjoyed them more. With that said, seeing Cliff Burton in 85 is still a special memory in that hind sight is 20/20 type view of things. When I saw them in 85 I just assumed this was going to be the lineup for as long as they would be around. When Puppets dropped and at the time it became a bit of an obsession of mine, I thought I'd be going to see Cliff with them when they came around. Less than two months before that show in 86 he was killed in that horrible bus accident in Sweden and being completely honest I went to that show thinking it could not surpass seeing them the year before with Cliff, but Jason played like a man possessed at that 86 show, he was doing his damnedest to fill the big shoes left by Cliff's death and perhaps that's what made that show so memorable. Cliff's absence was palpable, like something solid hanging over the show - it drove the band, it definitely contributed to the energy and the emotion of the show that night.
Certain band lineups are true classics either for the music they created, the time period and influence they had, or possibly for the stage show they put on. I could go on and on about certain bands that might have still be OK without certain members, but never as good as when those certain members are/were involved. Priest without Halford? Sucked! Black Sabbath without Geezer? While I enjoy parts of the Tony Martin era of Eternal Idol, Cross Purposes, Tyr, where Geezer was not involved on bass - Black Sabbath is better when Geezer is in the fold.
Another example - Slayer without Dave Lombardo is just not as good as Slayer with Dave on the drums. Paul Bostaph is a great drummer in his own right, but when I think Slayer, I think of Dave on drums.
I can't imagine thinking that it's not the people on stage that make a show great and they are all just interchangeable parts that if one goes down, no biggie.