Quibbling about late medieval Persian polities has little to do with "who won the Last Persian War".
The political result was a clear draw. Militarily, it is not so clear; a window of Byzantine vulnerability was taken by the Persians to score tremendous initial successes out of all proportion with any Sasanian military effort before, an effort primarily possible through Byzantine internal problems. Those internal problems were resolved, the Sasanians failed to finish their enemy off, and that enemy forced the Sasanian government to come to terms eventually. The overall picture of Byzantine military supremacy over the Sasanian empire is not in question; it is as silly a suggestion to claim that the Sasanians were militarily superior to the Byzantines overall as to claim the same of the Taliban as compared to the United States.
This does not mean that it would have been militarily and politically possible for the Byzantines to "totally defeat" the Sasanians, or occupy their territory; with small exceptions, such as Nisibis, that wasn't even desirable. The decisive element in weakening the Sasanian state and causing its political and military demise at the hands of the Caliphate was its own internal problems. The Last Persian War caused a tidal wave of civil war that wiped out most of the state's trained military forces and badly thinned the ranks of the dehgans. Arabic personal military prowess did much of the rest.