You cannot compare the two scenarios with a "what if". The 911 for a long time was Porsche's only car and the "breadwinner". Mercedes was never really a "Sports Car" manufacturer and their SLs were niche models in the line-up. And then, MB sort of kept a SL and improved upon its drivetrain.
The only time Porsche was running one car was part of 1965 with the end of the 356 through 1970 with the introduction of the 914. Porsche sold many more 914s each year than 911s during its production run. The end of the 914 in 1976 brought about the beginning of the 924, which likewise sold in greater volumes than the 911. Not because those cars were necessarily better (though the 914-6 is really something), as you know, but cost... By '78, they had three options. I'm no Porsche expert but I've heard the success of the 928 and 944 in particular really is what helped keep the company afloat. Much like their SUVs today... in fact, they sell so many SUVs, you might call them an SUV company and a sports car company second. They sell 4x as many SUVs as they do 911s. But we all think of the 911 when we think of Porsche, no? And hey, Volvo isn't a sports car company, but that doesn't mean they couldn't have been with their sweet little P1800. Anyway, point is, the sedans or station wagons and now SUVs are the bread and butter that keep the lights on, but in the popular mind, the halo car is what forms the nucleus of the brand's identity. Jag produced 72.5k XKEs across all series. Compare that to about 90k series 1 XJs, 50k Mark X/420Gs, 25k S-types, and a whopping 90k Mark 2s. That's 3.5 times as many big executive cars or saloons as sports cars (and is the series 3 XKE a sports car?). But you and I both know what comes to mind when you think of classic Jags, aside oil leaks and electronics. Perception! The 107 really isn't the same. It's a good car, but it's really uncool. Better than the XJS which was both uncool and not good, I guess...
I saw the same car back in 1997 with a 250SE engine in it. He opted for that engine to conform to the class he was running in. It's a bare bones car.
Bare bones is right! Yeah, I think he went from the 2.3 to the 2.5 and a 2.8 before the 3-liter 110.