AOR systems, and the historical vs the realistic

[bobbin]

Ofc that's what happened, the point was that for example in Britain, Crimea, Armenia and Mesopotamia didn't happened: rather soldiers from other regions were deployed there, that's what I've been talking about...
Afaik even in Spain and Gaul only certain areas provided legionaries, like the southeast for the former, Narbonensis, Lugdunensis and Belgica for the latter...

Well it didn't happen in the Crimea and Armenia because those were client states and so were not part of the Romans military administration, they undoubtedly would have furnished them with specialist troops for the Auxillia though. Mesopotamia was only ever part of the empire for a short period of time and so the necessary mechanisms were not in place. Britain on the other hand did provide legionaries to the army.

In your view given any people in any place, if they were ordered to fight in a demanded manner it would have happened, I disagree on that and imo it's about the local military traditions...

That is not my view, if there was sufficient access to manpower they could have trained them into Legionaires, that is what training is all about! They taught them how to fight in the Roman style, if that was impossible then you would have Gauls hacking away with their Gladius like it was a longsword, Numidians throwing their pila before running away when the enemy got anywhere near them and Iberians skulking around preforming hit and run attacks.

Why there wasn't any "adaptation" after Carrhae for example?
While roughly two centuries later it happened in the same area...
On one side you don't have any natives for hire and on the other you do...

But was adaptation after Carrhae, the use of missile units increased and horse archers were brought in (later being directly trained by the Romans). The eastern legionaries armour became heavier as well and scale mail became more common.

Nothing to do with Sauromatae and Alani for you?
Both being hired by Roma...

So? These tactics were being used to directly deal German armies, the Romans saw what kind of troops the Germans used and brought elements of their own that would be able exploit weaknesses in those armies to the region, that is adapting if I'm not mistaken.