How good are American roads?

A good comparison point would be Germany. It has a very large network of roads too, some designed for very high speeds, and a strong driving culture (perhaps stronger than the continental US).

I'm an American, I lived in Germany for several years around the turn of the century. German roads that I encountered were far superior to American roads. Their construction is far more robust, the roads last much longer. And with German lane discipline (passing someone on the right is practically a cultural taboo, it's a prohibition that's taken quite seriously) they are usually a joy to drive on.

I found the autobahn utterly nerve-wracking to drive on.

In the US, on an interstate, the MPH spread around the speed limit is probably -20 to +20 (i.e. limit is 75, slowest cars are at 55, fastest at 95)

In Germany, on autobahns, you have speed ratios of up to 2x. You have to constantly be 110% aware of every vehicle within 1/4 mile of you, because you could either be closing in the much slower vehicle in front of you, or suddenly approached and passed by a much faster vehicle from behind.

Absolutely. I was stationed in Germany for 3 years while I was in the Army. You could be in the left lane of the Autobahn, doing 90+ passing a truck, and suddenly a Ferrari that wasn't there 5 seconds ago is right behind you, flashing its headlights demanding you get out of the way (apparently you're supposed to merge into the side of a semi).