Yes, the interstate system was designed for 1950’s cars to be able to go 85 mph. These were automobiles without independent suspensions or computerized AWD. No disk brakes. Without electronic rack & pinion steering. Not to mention the improvements in tires themselves. Basically, cars were a lot less safe at higher speeds.
Now, my wife’s 2018 Honda CRV will slow you down and warn you when it senses that vehicles in front of you have slowed down. My buddies Tesla basically drives itself at 90 mph.
The only real issue is road maintenance. The fact is the autobahn roads were built with much more base depth than the interstate highway system in the US. Therefore, they are not subject to as much frost heaves. Also, do not even think about getting in that left lane of the Autobahn unless you are going 100 mph+.
The road maintenance part is important, I agree. Not too bad here in Arizona, mostly, but there are still some rough spots here and there. I just go with the speed of the surrounding traffic, and avoid the bad pavement once I know where it is.
Never have driven in Germany, though I’ve ridden as a passenger on the Autobahn.