If you purchase an efficient new car, then drive it into the ground for 15+ years, I suspect that the net costs for the period of time are pretty much a wash.
If you purchase an efficient *used* car, then drive it into the ground for 15+ years, I suspect that the net costs for the period of time are significantly less than buying new. Or if you purchase an efficient used car and drive it into the ground for 5-7 years, and then rinse and repeat for another 5-7 years, and rinse and repeat for another 5-7 years.
In my lifetime, I have owned 8 different vehicles. I still currently own three of those eight. The total purchase cost of them in total was ~$15,000. Or I could have instead purchased ONE new, very base-model economy car ten to twelve years ago. But then I would never have had a couple of really neat VWs, a useful minivan, a reliable economy sedan (Civic), a pizza delivery car (Civic) that just about paid for itself in fuel economy savings, a giant Dodge maxi-van that we learned some life preferences with, my SO's current car (Accord), or my work truck (Ranger). I'd have one car and one car only. And that would be significantly less value and utility in my life for the same financial outlay.
ETA: that $15,000 number is not counting any recouped cost from selling the five vehicles I no longer own. If I did count that, my total purchase cost looks more like ~$8,500.
This is also not counting the extra cost to insure a brand-new vehicle vs an older model. Or the extra expense of not having learned how to fix my own vehicle, for fear of ruining a new and very expensive (for a 17y/o kid) car.
I remember being 18, 19, 20, 21 and 22. Buying cars for $400, $700, $2000, $2000, $1500.
1st car had no clue about cars, period. Thing died immediately after the oil pressure light went on (seized motor). Lasted 2 months
2nd car, still no clue -> broke down and repairs would have been more than the car cost originally. Lasted 6 months
3rd car -> unfortunate accident where I hit a pothole just right coming over a hump in the road and there was a large metal beam sticking up out of the pothole. Bent the frame, destroyed the radiator, fan, bumper, front grille, etc. If I did have a new car with full insurance I would have been okay. However, this was too costly to repair even though I spent $2000 on the car. Lasted 1.5 years
4th car -> still not knowing enough, I was scammed into buying a car with a broken turbo and too tall tires. The tires, being way too tall, worn treads and had poor traction; I lost control on an interstate interchange hitting the guard rail at 50mph. Lost another $2000. Lasted 1 year
5th car purchased brand new at age 22 for $14,000 lasted 13 years. By this time I knew enough to be able to do all the maintenance on my own vehicles and could rebuild most anything on a vehicle (never touched an auto tranny though).
My anecdote, unlike your anecdote, indicates buying new and keeping for the long term is far superior in terms of cost. Maintenance was far far cheaper on the 5th car compared to any of the previous (no more distributor caps, plug wires, timing light, 3000 mile oil and filter changes, 12000 mile spark plug changes, 24,000 mile fuel filter changes, 24000 mile radiator change, 60000 mile O2 sensor - the new car required plugs at 100,000, oil & filter at 7500, no fuel filter change unless an error code is thrown, no special equipment to set the points and timing on the distributor, 60,000 mile radiator fluid changes).