I am not entirely sure on this one..... One issue the Umayyad will incur is the issue of massive amounts of non Semitic Christians who have previous loyalties covering their newly conquered land and then an extended border to be attacked. The Ottomans succeeded in the conquest of Greece, Bulgaria, Serbia, etc, not simply by might but they dominated Anatolia, the most important piece of the entire Byzantine Empire; without its Turcofication following the 900s-1200s, the conquest the Ottomans made, would be very unlikely and or weakly made.
For instance, the Umayyad for all its prowess, is going to be highly pressed on its various fronts, once expanded into Byzantium fully. Most especially, in the north, they will face the Khazar, Slavs and Bulgars. All of which will see this as an opportunity to attack or simply flee northward. Khazars for instance will likely be drawn into their wars with the Umayyad over the Caucus mountains and the Pontic Steppe regardless, increasing further the spread of Umayyad forces. Then, the Umayyad will conquer North Africa and perhaps Iberia shortly after and extend their borders immensely. The further possibility of a Khawarij revolt becomes more possible and prevalent, especially once you consider the vast numbers of people added to the Islamic world.
Frankly, this could lead to Islam being broken down even further. I actually can imagine a scenario whereby, Islamic states rule Iberia, Libya, Egypt, eastern Anatolia, Iraq, Arabia, Shams and possibly Sindh. This has Algiers, Morocco and parts of Tunisia breaking free from Umayyad rule by the Khawarij powers who likely then turn on each other, leading to a return to status quo in the area (likely to be conquered by Islamic states later/ as Indonesia was). Then, it becomes all the more likely for Greece to then transfer back to Christian powers or perhaps, Slavic or Bulgar states. This however, means that Aegean islands remain likely Muslim or Arab ruled, so that would include Crete, Cyprus, Rhodes, Corfu, etc... Then Iran could easily break off as was possible before the Abbasid Caliphate arose, whether this is a moderately Islamic state or Zoroastrian, who knows.