I would support that the emergent Roman successor states in Gaul, Britain, and Africa get mixed rosters. The area is not being liberated from 'Roman' control necessarily(They're all 'Roman' after all),but rather from control of the Emperor on the throne in Rome/Ravenna/Mediolanum(We should be able to change capital, but that's another matter to be addressed.) It's there more to be seen as local nobles/officials rising up or being set up as a puppet against the current Emperor/making an attempt for the throne. It is also odd that you can 'liberate' Romans from the Roman Empire. Of course, the culture left by the Romans did have a lasting effect on pretty much everything, but just have copy paste units to reflect this is nothing more than a lazy over generalization. The excuse being that Western Europe was Latinized by the 5th century to such an extent that the societies (and ergo the military forces) which rose up once then WRE had collapsed were identical those of the late Empire. The short answer is that CA were too lazy to make dedicated units for them.

2K A Total War Saga: Thrones of Britannia.

844 A Total War Saga: Fall of the Samurai.

Total war attila roman units