Source: Messages on the net.
When were they successful? Apart from Belisarius conquering a chunk of Italy and Maghreb, they never did anything else. Just continuously lost land and stagnated despite having the entirety of Greek science at their disposal for 1000 years. Their brightest moments came in 717 during Siege of Constantinople and in the 6th century. Although even in the 700s they only won defensively. They lost most of their lands to Ummayads.
Even greek independence came due to phillhelenic westerners and teutonic powers fighting ottomans for greeks. In 1924, Greeks somehow lost to a defeated Turkey despite having France and England on their side. They had chance to conquer Anatolia permanently but got beaten by a battered post WW1 Turkish Army. Overall, just a pathetic display of martial valor.
I suspect also that modern greeks and balkaners are probably the lowest IQ Europeans (low 90s)
Westerners reached renaissance in < 100 yrs after getting back hellenic science and philosophy. For 1000 yrs westerners only had access to 3-4 texts in greek philosophy and science - no euclid, no galen, no plato, etc.. Byzantines had all those texts and did nothing, science came to a halt for 1000 yrs in greece. Modern Greeks / Byzantines are somewhat like late medieval Hindus but x100 worse. Militarily unsuccessful, and scientifically unsuccessful.
If you look at Byzantine theology, you’ll realize how anti-intellectual it is in a way. This is completely unlike Western Christendom. Byzantines focus a lot on monasticism, visions of god and supernatural yaugika pratyaksha but hate providing arguments for their theology unlike in vedanta. Although I will say byzantine theology is closer to H view of God than Western Christian - exception being Neoplatonist western mystics like Meister Eckhart. Orthodox xtians are similar to muslims, very zealous people. Only difference is that orthodox have been militarily less successful than turks intil russia came to front stage.