Ahh, I could not be denied a comment or three here. Great first paragraph, by the way! Loved the historical parallels!
As a fan and former owner of several examples of both the Mercedes 300SEL 6.3 and the 1973 Jaguar XJ12 (the only year for the SWB Series 1, by the way) , I think I have something to add.
The review here was fairly accurate, but it reflected the characteristics of only two examples, whereas I've owned three examples of each.
First, I agree with the styling, design and interior environment analysis here. The beauty and grace of the Jaguar leaves the Kraut tank on the trailer. However, referring to the Jag as a "limousine" is quite erroneous as its delightful short wheelbase pleases the outside observer far more than the rear seat passenger. The LWB Mercedes was far more commodious.
As a sidebar here: Jaguar wood veneering surpasses the tissue-thin Mercedes stuff. Mercedes leather surpassed the (not Connolly!) surface-died Jaguar hides. Neither had switches worth a damn. Never compare the quality of either of these cars with a Rolls-Royce or Bentley—you're revealing your seduction by the genius of the marketing departments and manufactured perception of both Jaguar and Mercedes. I've had all four marques to pieces and the Crewe cars hide hardware—unseen behind the dashboards—the equal of jewelry.
The Jaguar's engine was far more refined. The Benz felt like someone dropped a SBC in it, as its power came on in an uncharacteristic rush. The Jaguar was a seamless rheostat of increasing G-force. The Mercedes trans was far better (as mentioned here) than the under-spec'd slushbox in the Jag. By the way, I've driven a Series XJ12 with a 5-speed Getrag. O...M...G...what might have been!
Handling? Did someone here say the Mercedes outhandled the Coventry product? The comment, "The Jaguar shows even less appetite for the corners than the Mercedes" might be subjective, true, but not in my experience. The Mercedes—when its air suspension was in good nick—had a fine, albeit stiff ride quality. But give me the Jag on Topanga Canyon from Ventura Blvd to Pacific Coast Highway, and I'll be sipping a gin 'n tonic at Mastro's before the Mercedes pulls in, tortured tires still smoking.
Even with current values considered, I'd still prefer to have my best 1973 XJ12 back in my stable than my best 6.3.
~ Dave Destler