What we need to know:
1st: For laong time soldiers of both parts of the empire were of Germanic origin and not native ones!
They may used Roman equipment or/and tactics but Roman citizens were no longer the recruitment pool of both of Armies.
Example: Officer of infantry in Justinian's Era:

Watch carefully the "germanic" spears with the famous german (or later known also as slavic) spearhead!
Also nottice the Seax knife of that warrior!
The rest of his equipement is Roman of the 4th-6th century!
An other example: "German" officer of teh same era!

This guy also uses Frangiska axe exept the Seax knife!
The 1st real native Roman soldiers re-emerged under the will of Belisarius but not in the era of Attila game!
Banner man of Justinian Era:

Some one mentioned that East Roman troops (of that pic) look more or less like Sassanids!
Lets make this clear! Romans affected (in the east) by Parthians and later by Sassanids! In fact eastern Empire coppied several aspects from Sassanids!
The Roman Emperor was "King of Kings" just like the Sassanid Sachansach! The Roman cavalry adopted many tactics and equipment from Sassanids and much later from Avars!
I still don't get it why CA insists with the Palaelogian Aquilla instead of the Cloasic Aquilla for both Empires of it could use the XP sign (like the banner man) again for both empires!
Why CA tries so hard to show that Eastern Roman Empire was not Roman at all???
Gothic King of Spain:

Goths (espesialy in Italy but mostly in Spain) adopted much of the Roman administration system .
The Roman influence in his armor is the leather background of his "steppe" kind of lammelar cuirass!