Hence what I'm saying.
From a purely environmental perspective the person who bought a car in 2017 that has the financial means to get a new EV car would be better off getting one, selling their 2017 to someone who drives a 2005 that would sell to someone that drives a 2000 that would send their car to the scrap yard or keep the chain going. Your analysis implies that the 2017 car gets replaced and doesn't get sold to someone else, either the owner keeps it and doesn't drive it or it gets sent to a scrap yard, which isn't what happens in reality.
The point is, it's better to intentionally introduce a new car on the road that emits zero pollution (or close to) and that allows us to get rid of an old car that emits tons of CO2 every year even if it's still drivable than to just wait for the old car to die to get the process going from the bottom up.
I could make a complete mathematical breakdown to show it but I've basically already done it in another comment just with two cars instead of a long chain of cars.
Funny you should mention sunk cost because it's a sunk cost fallacy to say we shouldn't get these cars off the road just because they've been produced already (as long as the total number of cars stays the same in either scenarios, just to be clear).