From my pov I think you’re repeating exactly what I said, but I appreciate the additional details.

My last point is that “the design life we choose” is usually dictated by non-engineering forces. A 12th century king can throw resources at a problem. A 20th century governor cannot, and doesn’t care to. They care about the bridge lasting until the end of their term limits.

Labor was free because of slavery, so the economics were not the same. Current engineering has the concept of “over engineering” which is what cracked-up addicts in wall street call “building to last”, due to the “expense” of not being shortsighted on a quarter by quarter basis.