The car analogy doesn't really work. Sure, it's probably true for the Big 3 and their Japanese and Korean counterparts, but companies like Ferrari and Lamborghini don't sell any mainstream cars, only ultra-high-end performance models.
Ferrari is owned by Fiat, which also owns Chrysler/Dodge.
Lamborghini is owned by Volkswagen via it's subsidiary Audi.
Could go on with that. Jaguar = Ford, Bentley and Rolls Royce = Volkswagen, etc.
Most of these companies were absorbed by the larger mass market auto groups for a reason, and it wasn't because they were viable and profitable in and of themselves.
Anyway, it's worth pointing out that (as you note in the first paragraph) the GTX 970 is basically a mainstream GPU; sales are massive by all accounts, far exceeding even Nvidia's expectations. And assuming the Broadwell ~= GTX 750 comparison is roughly accurate, you need to at least triple Broadwell's perfomance to get close to GTX 970 levels.
And while the GTX 980 Ti is no doubt a much lower selling card, sales aren't negligible; it's reported as being sold out almost instantly everywhere. ..
I agree the 970 is a midrange price bracket card - barely.
People lose their perspective because of all the hype on these high end cards.
Point in fact, when you look at Steam hardware surveys the GTX 980 gets a whoppping - 0.69%. Yes, two-thirds of one perecent, on a survey that is almost certainly weighted to the high end.
There are more Radeon 5450s in use on steam than 980s, more GT 430s in use, more GTX 640s, etc etc.
This super high priced, high end mess is relatively new. Go back to the days of the GeForce 256 - a $299 card.
This is what AT said about it in Dec 1999 :
"The DDR GeForce is everything we expected from the original GeForce,
unfortunately its high price tag [edit: $299] will keep it out of the hands of many. "
So in real dollar terms, $299 then = about $350 now.
These $500+ cards are interesting, but it's not where the money making machine is.
If Intel starts really eating up the bottom, like obsoleting the R7 250 or the GTX 740 / 750, AMD and Nvidia will literally be getting eaten feet first. Intel will not need to get anywhere GTX 970 levels to kill those companies.
If they get 750 Ti levels it will kill off the entire AMD R7 line and blow the bottom end out of Nvidias lineup (look how many x30 and x40 and x50 line cards are sold).
It would probably kill off the R9 270/270X and GTX 960 as well - after all, they're faster, but not so much to justify the expenditure for most people.
And once you get past that point, it's just the high end peanuts left. AMD might actually outlive Nvidia in that scenario, because AMD has its APUs.