There has never been a time in history when the Iranic people were united in one country.
The Scythians never completely came under Persian rule. Even now, Kurds, Tajiks, Pashtuns, Baluchs, Azeris, Persians, etc. are not united.
From the time of the Arab invasion to the Safavid era, Iranshahr was not exist in political maps.only there were Iranian dynasties that were successful only in one region.
Safavid once again revived the concept of Iranshahr, with the help of Shia Islam.
Safavid idea is masterpiece in history, they created neo-iranian empire in only possible way, preserving portion of persian culture and iranian imperialism, with shia islam area of influence...in europe, many scholars view concept of finalizing shia islam as iranian revenge for arab's conquering, or - persia strikes back...iran became leader of it's former invaders, key player from the persian gulf to mediterranean sea, ancient sphere of influence for iranian nationhood...i read one great dissertation "islamisation of iran - iranization of islam"...
And from any point of view, this 3 pillars, iranian institutional tradition, persian culture and shia islam are making iran such melting uniqueness...and way to preserve major regional power ...
Which other way is possible for iran? aryan land concept? Very hard way to project power to Tajikistan, and part of china and russia, having turkish state as rival also... so, conflict with 3 major powers, for barely useful area....
I mean, in geopolitical sense, this way of iranian projection in west asia, or middle east, crucial global region btw, is geopolitical masterpiece, shia islam is iranian interest more than vice-versa...I'm writing this as iranian fan, in love with persian culture and ancient empires...just my honest opinion...cheers