You're comparing total numbers of deaths while traveling on highways, which means you need to also compare total passenger miles traveled on highways. Using per capita is utterly absurd. I'm not saying that you're automatically wrong, but your current argument statement is incoherent.
AND ALSO, 40% of the autobahn has speed limits, trucks are always limited, and advisory limits apply everywhere according to https://www.deutschland.de/en/topic/life/germany-and-the-aut...
The link also says "In practice, this means that there are only a few stretches of road where you can really drive at unlimited speeds during the day."
AND ALSO, speed limits aside, what's the actual average traveling speed difference between the two countries for passenger vehicles? The same link says the average in Germany is about 78mph. Ask someone living in the US if that's significantly faster than here.