Why wouldn't he toss his pilum at the Hun's horse and then stab rider on the ground?Yes I definitely think the sudden uptick in Cavalry coming from the ERE, Sassanid's and the Hun invasion would of been a massive problem for the Gladius wielding Classical Legions.
The fact that the legions took on basically all the weapons and armour of the Roman Cavalry soldiers speaks volumes.
I also think what me and Aggie were discussing as in the need for a border troop policing the Empire over a conquering aggressive legion also was a big factor, the Romans became more defensive rather than offensive and the classical Legions were designed to steam roll other infantry armies.
The weapons of the late Romans was more for an individual warrior with longer reach, but could also band together in a shield wall.
The Classical short reach against this influx of armoured and long range cavalry would of been a definite issue.
I think all that combined I can form an idea now of why they deviated, Infantry vs Infantry was not the be all and end all of warfare in the Dark ages that it might of been in Classical times especially in the West, Eastern style horse warfare had arrived from both the Middle East and Far Eastern Steppe hordes.
Just picturing a classical Legionaire with a Gladius trying to fight off and hit back against a Hun on horse back is an issue right there.