I’ve begun answering your question five times and stopped each time. They all come to the same conclusion. I just don’t think it matters. A great engineer records the sounds to match the song and if he’s great, and the performance is great and the song is great, the sounds will be great. Give him all the same pre’s or put a hundred different ones in front of him and I guarantee he’ll experiment. And when the recording is done, it’ll sound great whether it was recorded with one or 10 different pre’s, because he’s using them to mold the sound to what is great for the song. If you’re going to hear one instrument sound out of place, it’s either intentional or because the engineer didn’t get it right, not because of a pre of any kind.
Would Led Zeppelin or the Stones have sounded any better if Andy or Glyn Johns had twenty pre’s to play with back in the day? No. They get an instrument or vocal sounding great because of a combination of factors; right performance, right mic, right positioning, right tuning, right compressor, right pre, right EQ etc. Throw the Pre’s into the mix if you want, it doesn’t change the over all picture.
I would be surprised if, in retrospect, guys like AL Schmidt, Phil Ramone, Andy and Glen Johns, Hugh Padgham, Tony Bongovi or any of these top level engineer/producers would have felt they could have made better sounding records with the addition of a multitude of pre’s. I think the focus seems to be misplaced on the toy instead of on the guy behind the toy.
To address your final question, when I mix a song that sounds great, it’s because it was well recorded and the choice of sounds on the instruments are perfect for the song. That’s all that matters to me.
I’ve mixed songs recorded in a house that blew away tracks recorded in great studios by crap engineers.
When I get tracks recorded by George Massenburg or Jay Messina, I’m a happy guy. I know for a fact they’ll do the right thing and record it in a way that suits the song.