Apparently, the Intercisa is several decades after Palmyra, so it could be ruled out. Nor is it a closure.
Intercisa appears as a response to the economic collapse of the Roman state and the adoption of new manufacturing techniques.
https://imperiumromanum.pl/en/curiosities/fabricae-roman-armory/
Intercisa is definitely out.
It is due more to the financial collapse of Diocletian's time.
Forging a spherical bowl in a single piece required highly skilled artisans and many hours of work.
• In contrast, the Intercisa design allowed less experienced workers to cut prefabricated iron sheets, join them with a central riveted band, and assemble a functional helmet in a fraction of the time.
"With the third century A.D. and the growing threats at the borders, the design of Roman helmets evolved towards simplicity, pragmatism and low cost of production. The steppe and Sassanid Persian influences began to be noticeable, especially with the reorganization of the army and the appearance of government armor factories".
Regarding Eastern archers:
The lighter archer levies, or those raised in emergencies, used caps of pressed felt or hardened leather.[[Here I will need a source to validate this]
The movement of the bow: When drawing an Eastern composite bow, the string is pulled back brushing against the cheek or the ear. If the archer were wearing the enormous metal cheek-pieces of a Roman legionary, the string would constantly strike against the helmet, deflecting the arrow and ruining the shot.
Some helmets with this description would definitely be ruled out.
https://www.romanarmytalk.com/rat/showthread.php?tid=17085