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Let's assume that there are two ATLs, both are revolving around the Byzantine-Sassanid War of 602-628:
1. The first one is where Heraclius got more luck than in OTL and successfully incorporated Mesopotamia and Armenia into the Roman Empire in the aftermath of the OTL "Final War", while the Persian Empire collapsed into several warring states.
2. The second one is the exact opposite: Khosrau II successfully captured Constantinople, and there are several Roman successor states scattered in Mediterranean.
The question: assuming the Muslim invasions still happened as per OTL, which one that have higher chance to successfully repel them, the Byzantines in the first scenario or the Sassanids in the second one?