I am listening to Mike Duncan's podcast titled "The History of Rome" and in it he mentioned that it is kind of a mystery that the Huns were so successful at siege warfare but the Goths were not. Both were considered barbaric tribes and yet both tribes had leaders who had served in the Roman army. This is an important factor as it would allow both, the Huns and the Goths, equal access to the knowledge of the methods the Romans used for warfare and siege defense.
That the Huns were superior warriors (perhaps because of their mounted archers and their legendary bows) as compared to the Goths and their contemporary Roman counterparts, is not a part of the mystery. So the real question is: how did the Huns, unlike the Goths, manage to breach the walls of major cities (except the Theodosian walls of course)?