Man, you want to try reading a book or two. You are completly wrong about pretty much all of your assertions.

For instance "Barbarians" DID build roads, in fact the Ptolemeys for instance built roads that easily rivaled the Roman road of the time. It is indisputable that Rome EVENTUALLY became the premier road builder of the ancient world, but this is a far cry from a monopoly. Even in Gaule, road construction was undestood and practiced.

As to sieging the various peoples are represented roughly accuratly, (in reality it was less an issue of engines but of logistics anyway)

Your third point, about naval advances misses the crucial difference between the Atlantic and Med. (to be far so does the game). Each tech developed speratatly (as you'd expect) and to compare one to the other is pretty much a case of apples and oranges.