That is correct, the median speed, as a rough guess, from the pizza place near my house, to my house, would be 35mph, including the 2 stoplights in the way. Assuming we had proper bike infrastructure(which we don’t); you’d be hard pressed to top the speed a car can go, and you would still have to stop frequently at lights, just like a car. And remember, that is the nearest place, not the only. And a small sub note, this area is not flat, at all. The gradient changes are brutal for bikes and they can’t sustain a decent constant speed. Well, at least before electric bikes.
I am not defending, in any way, America’s horrible car centric infrastructure. It is what we have though, and as a result, bike deliveries aren’t an option for the vast majority of America. Of course, when you leave the city, it gets worse.
Something else you seem to be missing is often, a lot Americans live off highways. 20 miles may only take 20 minutes of drive time. When I lived in slightly more rural area, most driving took almost exactly minute per mile. Our entire country is designed around vehicles moving at high speed. My city is wrapped in a 60 mile interstate. An unbroken loop around the city who’s speed limit is 70mph. Outside of rush hour, you can take it all the way around at 80mph without ever braking in the slightest, unless there is a slow moving car camping the passing lane.