All sympathy to the families involved; what makes this the worst auto scandal in history? Are there numbers for this or is this based on public opinion?
I think it's exacerbated by the lying, the cover-up, the myriad missed opportunities to fix this as the dead and maimed piled up. It's like Fight Club's ABC quote, except the math pointed to an obvious recall situation and you guys thought you could get away with it anyway.
To me it's a tremendous blow to GMs entire credibility as an auto manufacturer. Basically it paints the company as a bunch of crooks which couldn't care less about their customers. I mean, when I get in my car, point it down the highway and accelerate to nearly 100mph, there's a fairly high degree of trust which I'm placing in the equipment. When it's revealed the degree of apathy GM has for its customers, it tends to erode that trust.
Over 1000 claims of bodily injury, ~74 dead, because you couldn't ship a proper ignition switch, and didn't feel like fixing it when it became obvious. It truly is shameful.
"[...] if you took all of the cars that GM has recalled this year and lined them up bumper to bumper, you’d end up with a line that would wrap around the earth four times."
Bronco, Explorer, and F150 rollovers -fixed by adding stability and Tire pressure monitors
Toyota's gas pedal and floor mat recall - halfway similar to this issue in that it involved very poor affordance (drivers could not immediately tell what was wrong, they thought they were pressing the break, but the gas was pressed as well)
GM Streetcar conspiracy
Cars from the Big 3 used to literally fall apart in the 70's due to poor assembly. (Welcome Toyota)
Ford Pintos in the 1970s had badly under-designed gas tanks that ruptured and caused fires in rear-end collisions. Media put the death toll in the "hundreds", NHTSA had a death toll of 27.
The scandal of the Big 3 killing smaller car companies like the Tucker 48.
Incredibly stupid design decisions like planned obsolescence.
GMs policy of "build a bunch of cars and make people buy them" from the 1970's to the early 2000's - responsible for peoples poor opinion of GM and competitors that followed the same mantra (It even bit Toyota in the mid 2000's)
The only one on your list which is comparable is the Pinto, where a known fatal fault was cynically ignored because it would be cheaper to keep paying out on lawsuits than fix the problem.
Disclosure: I have been a GM employee since 2013