This is the Lincoln Memorial:


This is a reconstruction of the Statue of Zeus at Olympia:


This may interest you as well:
https://en.wikipedia.org/wiki/Parthenon_(Nashville)
Not sure why Old World buildings at that time would have different construction techniques. One project which would have been quite unique was the Koln/Cologne cathedral, which was started in medieval times but not completed until the romantic period. Plenty would have been wood frame. Old World also had to deal with WW2 happening at a time when aircraft technology was very advanced but anti-aircraft technology was very primitive, hence everything got bombed constantly for 5-9 years.
The domes are so popular because in the late classical and early medieval period Constantinople was a symbol of power, tradition, and Romanness and every king or emperor did their best impression of a Roman Emperor and tried to rival or outdo the Hagia Sophia in Constantinople. The Hagia Sophia's innovative vaulted dome was impressive and at such a scale was an architectural marvel. So tons of stuff copied the Hagia Sophia, and Romantic era architects copied that stuff. Spires basically just look nice and make a building much taller/grander in a cheap and artificial way.
I also hope to see the flip in my lifetime, though typically such inversions happen when the current model crashes and burns, which at least in America probably wont happen in the next 50 years. Canada, France, and Sweden are ground zero, we might get to see these places go up in flames but any kind of break away from the American imperial order will likely be quashed.
About your question on empire, the Greek philosophers had their own answer 2K+ years ago, the idea that the ideal society was one with a philosopher king. Rome eventually manifested this dream when Marcus Aurelius, one of the greatest stoic philosophers, was their emperor. It was however Aurelius himself who made sure this did not continue, as he was the one emperor who instituted the rule of hereditary succession. Thats right, the same old model that kings and even tribal chieftans have used since the dawn of time. His son Commodus was a pompous ass and fairly poor ruler, so indeed we were in every sense back to the basics.
Rome was certainly wise, but certainly not benevolent, truthful, or "good" according to some kind of morality. I think it was their wisdom that showed them how cut-throat the world was, which made sure they were not especially friendly. Does power always corrupt? From a modern perspective the answer is probably yes. People in power will use that power to look after themselves and their immediate family first and foremost. When being in power is a cushy office job where culpability is often superficial and only lasts 5-10 years before someone is blaming someone else, its easy to understand why we hate this. Traditionally, being in power and getting your family rich was understood to be human nature, thus we created institutions which codified this and gave them additional responsibilities. This created the warrior aristocracy class, the Kshatriya. In exchange for their wealth and privilege they were leading the charge at the frontlines of every battlefield.
Corruption of course can extend far beyond just using your power to get rich and get your family rich. When I think of corruption I think of a lot more than that. To put things simple, you can expect the commoner to be less rich than you, but you shouldnt be selling them or indeed your entire civilization down the river to get rich. This is a corruption which exists also as a kind of treason and perversion. It can only manifest in a mind of unnatural filth and degeneracy, or alternatively an enemy infiltrator. Does empire necessitate all this? Nope, or else no empire would last more than 200 years, yet plenty lasted much longer.
As for Hitler, I think he got some things right, got some things wrong, but ultimately his project got cut short so we never got to see a proper manifestation.
Also to be clear Rome had plenty of treason and degeneracy itself, it was excellent but far from ideal. For me what gave Rome such a crazy legacy was that it was so good at adapting to all of the crazy problems it was constantly facing. Of course their luck didnt last forever though.