It is posssible that the slope of the curve dramatically reverses sometime between "no seat belts and stiff steering columns" and "literal spike in the middle of the steering wheel" but that seems unlikely and there's no reason to think that would happen.
Our perceptions differ then because when I drove an old Plymouth without seat belts, I didn't drive it as gingerly as driving a modern car today with a birthday cake in the front seat. A literal steel spike into the heart would make me more cautious than worrying about a birthday cake slamming into the dashboard. The Plymouth's steering column never gave me the feeling of impending death but a literal spike would. I think that sharp point on the end as a constant reminder really matters for the thought experiment.
Yes that is true but it's not relevant to the idea that an alternate universe with different conditions could be safer than seat belts. If one truly engaged with the thought experiment, you'd have to try to imagine all side effects of the "ludicrous" spike. E.g. drivers no longer tailgate at 70mph -- in fact, they may drive under the speedlimit of 55mph. Instead of whizzing through the neighborhood at 40mph, they drive less than 20mph because any random squirrel running into street would trigger a reaction to hit the brakes which causes the heart to be pierced. Maybe less parents would let their kids have a drivers license at age 16 and instead make them wait until age 18 because of an iron spike pointing at their kids chest would keep them up at night. (That's 2 years less of teen driving fatalities right there.)
There may be all sorts of hard-to-imagine secondary effects that would lead to less deaths than seat belts. That's the idea of truly playing with that thought experiment. It doesn't mean we'd ever realistically implement that idea.