There is no doubt that Umar al-Aqta gaining a victory or at least avoiding a total defeat and his death, would have benefited the Paulicians. The Paulicians were a major contingent at Poson/Lalakaon and previously had long been a massive portion of the forces that Umar al-Aqta used to wage war with Byzantium. Their survival was tied to the situation on the Byzantine border and either Byzantium or Abbasid sides gaining total victory in Anatolia, would have spelled their doom. If Abbasid forces pushed passed the frontier indefinitely as the Saljuqs did, the Paulicians would lose Worth to the Islamic house and be persecuted most likely. Byzantine victory is otl, with the Paulicians losing with Umar al-Aqta and then losing consecutive other battles with Byzantium later that year.
Umar al-Aqta himself was an Arab emir and warrior of legendary status who rose to prominence in the Amorium campaign during the 830s in the regime of al-Mu’Tasim (838). His role under the Abbasid hegemony whilst not especially explicit, was clear enough. That is, a Ghazi, one who makes raids and wars on exterior borders of Islam with intents of raiding. This is also a muhjahid or one who partakes in physical jihad. Umar al-Aqta exemplified this title sublimely in the sense that he was extremely effective in constant raids that usually amounted to logistical strikes upon various Byzantine supply lines and then of course, constant strikes on villages and noble households for loot and slaves.
The issue with Poson, was that the elusive Umar al-Aqta who endeavored to avoid such massed battles was placed in a difficult position. This position being Poson, where due to Supreme Byzantine skill in planning and or luck, they were able to march contingents of the Byzantine army from three different directions, effectively closing in on the forces of Umar al-Aqta. The affect was that the smaller force of al-Aqta numbering somewhere around 15k was surrounded by an imperial army of 50k, Umar al-Aqta seems to have had a total mishap tactically and failed to receive word of the Byzantine movement from three directions, or else he would have fled. A critical error that would cost the Abbasid hegemony nearly 20 years of progress on the Byzantine border.
Regardless, Umar al-Aqta surrounded, attempted to capture a hill from which he could use to hold and then wait to attempt a breakthrough using high ground. This conflict over a nearby hill would occupy the entire first 24 hours of conflict, with vicious battle on the high hill. One can imagine the sheer will the Arab troops had in their frenzied advance on the hill, fighting with bloodlust to survive and have the hill. Despite the frenzy of the Arab troops, the Byzantine forces were able to push the Arabs from the hill and completed the encircling. The next 24 hours saw the continued tightening of the noose around Umar al-Aqta’s neck, as a python who chokes and constricts, so was the Byzantine forces strangling the Arab force. Umar al-Aqta and his men were undoubtedly experienced and skilled in many battles on the frontier and certainly knew their dire position. Failure to take the hill means that they will need to make a breakthrough on level footing with the enemy, instead of making a breach when moving down from a high position, as had been done by the Byzantines at Anzen in 838, which Umar was present at. However, on level footing, breaching was most difficult.
Regardless, Umar al-Aqta in the final hours of the battle, attempted a breach and struck headlong into the western edge of the Byzantine forces. The result was total defeat as the Byzantine forces stood their ground staunchly and only a handful of troops broke through and escaped into the hills moving west. Umar al-Aqta was cut down along with his men in the breach or in the Byzantine counter, once the breach failed.
The results of the battle was Byzantine complete annexation of Anatolia and eastward push uninhibited by the now abolished Emirate of Malatya. Abbasid hegemony to the south, struggled to counter these occurrences, but was unable due to internal strife and malaise. Byzantine ascendency was assured.
Had this not occurred, the affect is that Abbasid border integrity remains at least until 870 perhaps, before a Byzantine offensive strikes. In other words, while Abbasid borders can be held post 863, the situation in Iraq and Iran is very volatile already and the affect is strife that lowers the chances of more muhjahid arriving in Malatya to gain loot and also the lessened chance for an Abbasid invasion of Byzantium.