Isaak with a loyal army would never suffer a defeat at Manzikert;Romanus D' Diogenes in the actual battle in 1071 led a great army,but he was betrayed during the battle when his army was victorious, by his reserves led by a man who served the interests of Psellos and Dukas,the old status quo that Romanus had tried to eclipse...
Expansion? not in the East...by the way,what Romans?they didn't exist at that time,the term was used diplomatically to exercise influence in the West...
The Byzantine Empire called itself the Roman Empire, they were Romans in their own eyes, and although they spoke Greek, this was done in the eastern parts of the empire long before the split. It was actually rather the opposite of what you describe; the HRE called itself the Roman Empire to exert influence in the west, and the term 'Byzantine Empire' was only coined by historians in the 1500s as a way to make them seem less worthy of the Roman heritage.