What's "successful"? If the Romans seem to have been more successful, how does that make you feel, compared to, if someone made a convincing argument the Romans were less successful?
Reading about the Byzantine Empire just now[1], I'd say 476 to 867 was one "dynasty", because in 867 marked the beginning of a Macedonian dynasty, which lasted until 1025. This would break down the Roman empire into dynasties of length not unlike Chinese ones. How do you feel about that?