A few days ago I was listening to a YouTube video, and the narrator said "The Byzantines remained stronger than the Sassanids throughout most of their history". This seemed strange to me, as judging by most Byzantine-Sassanian wars, it was the exact opposite. Anastasius, Justin and Justinian all suffered heavily against the Sassanids, and always seemed on the back foot. Tiberius and Maurice seemed to have relative success, and they were focusing all the resources of the Empire on war against the Persians. And, of course, Phocas and Heraclius were barely getting by. So, what's the historical consensus? Who was stronger and why?
Stronger is a bit vague and might pose a problem for someone interested in answering. By stronger do you mean raw military might? That's kinda hard to gauge aside from the metric you've already used - victory on the battlefield. Are you asking if there were other factors that might have prevented the Byzantine Emperors from going all in on the Sassanids, or are you asking if other factors like trade or political influence outweigh military defeats? Military strength on its own is very hard to measure. It's even more difficult to measure the full power of an empire. If I'm not being too bold, might I suggest that you're asking what enabled the Sassanids to enjoy repeated military success against the Byzantines, and how either power would have measured themselves against the other?