...pretty much in furious agreement!
There's little doubt that those 6.9s were intended as the epitomy of Mercedes-Benz engineering. It is cars like that that helped them with their reputation for solidity. Your example of leather is very apt. The hides used for cars such as these were likely benchmarked off proper furniture, not the cheapest split-skin with vinyl facings that would allow you to put 'leather seats' in your brochure.
Relatively minor elements of those cars (and I include the early Porsches in this) such as door hinges and locks were made to a standard that would see other cars with sagging frames (I don't want to even think of those 70's disco interiors...fortunately, I've been spared spending much time at all in them)
The sterile comment concering the 2500 comes from a background whereby the earliest family car I can remember was a Riley 2.5, followed by a Triumph TC and a brace of Series 1 XJ6s...compared to which the BMW did seem sterile and less handbuilt. (we won't compare the reliability or the quality of those cars...ahem....
And finally, the comment on the 6.9s output wasn't meant to denigrate it. It's just a sign of the march of technology. I am not a particular fan of modern engines, but I cannot fail to be impressed by the combination of output, reliability, low fuel consumption and emissions that modern engines (even humble ones) possess.It just goes to show how much has been learnt and how much has been applied.