I think a lot of people will benefit from my answer to this question, since I had not been able to write for quite a long time and people have most likely forgotten details.
It's been a while since I've read this TL and I've forgotten quite a bit of the details. Could you remind me why Nikephoros, John and Basil have done so much better than OTL (Which they were already pretty successful)?
Mostly luck (in avoiding bad luck) at a couple of critical junctures.
They are still mostly the same people, but they avoided the major slumps in that period and are pushing non-stop, sorta like the Republic in the first and second centuries. Phokas actually did not get much done himself. The POD was that he felt Constantinople needed his attention more than Anatolia, and so he sent John east, who was younger and (from what I can see from his brief reign) quite a bit more aggressive. Not major changes overall from OTL in territorial terms (Aside from Sicily, the rest of the red in the map is OTL although might be a couple of years ahead of OTL), but it was enough to unnerve Phokas who sent John to Sicily, where he met George Maniakes levels of success reasonable in my mind). Phokas on the other hand really fucked up the situation in the Balkans (due to having a substantial number of troops in Sicily) compared to OTL, leading to crushing defeats and finally resignation-paving the way for John to seize the power. I also had the Phokas family potential rebels (Leo and Bardas) die in the Bulgarian campaign to make things smoother for John, who becomes Basileus and wins against the Rus ans Bulgarians at Arcadiopolis (exactly as OTL, even dates-the Balkans blue not much different from OTL).
Meanwhile the Fatimids had a slightly harder time getting Egypt (I think I made them 2-4 years behind schedule)-not unrealistic, since they failed a couple of times in OTL too and just waited to get their house in order for a final push. This means the Levantine states lack a strong protector, and that, coupled with Roman naval dominance meant that Tzimiskes faced fewer issues in his second set of eastern campaigns. Nonetheless, I again kept the gains mostly similar to OTL (these were lost in the chaos of the first twenty years of Basil's reign in our timeline). Then he does not die when Basil Lekepenos wants him to (big POD).
A couple of minor PODs along the way had been Tzimiskes earlier (960s campaign) had poisoned ground relations between muslims and christians via wholesale expulsion, massacre and forced conversion of the former (y' know, standard ethnic cleansing, nothing to see here), while using kid gloves for the latter; and him actually having a biological kid in Syria. Said kid ends up married for Basil for dynastic stability, and Basil-having nothing to do since John is alive and well, decides to go check out Anatolia. He quickly realizes that he doesnt have too much power, and works to correct that. Baghdad was his major lucky break (the Abassid Caliph did in fact ask for his help against the Shia Emir, only to well, get burned), making him a bit irreplaceable. The already deteriorating Christian/Muslim relationship in the Levant gets worse after this (killing a Patriarch-same as OTL btw- does not help much), and the powder keg blows up soon, with the Empire and Fatimids fighting it out. Both are aided by (muslim) Bedouin tribes, who have not dealt with the issues their urban cousins had been facing for the past twenty years and will go the side who pays best. The Romans are that side, unfortunately. Continous fighting with a Roman coast and a Fatimid interior, until the Romans get complete naval dominance with Venetian assistance (attack on merchants in Egypt) and are able to invade the Delta. The Caliph loses his nerve and retreated (bad move, the Romans had limited ability to deal with him in the interior, but he did get scared about his supply train vanishing), leading to a crushing Roman ally victory in the Levant.
The West was described in the last update. The cometopouli fighting is similar to OTL, and John simply makes Samuel a better offer than a distracted court OTL could. Arab-Roman de-facto alliance in Southern Italy is also not new news, but it just played out in a way to make it work out better.
So the major differences from OTL is that:
1. Higher interfaith tension in Levant, making it easy for Byzantines who claim to champion the majority community. No one actually believes that, but they seem like they will be distant masters than the ones killing your family right now. Some radicalization, and the Syrian Church nearly collapsing (easy target for both muslim mobs and Imperial agents) helps.
2. John actually living, and giving the Empire two hyper-competent Emperors at a time in OTL when they had one young boy fighting to survive. 976-990s was essentially a huge slump for the Empire, allowing Bulgarians and Fatimids to gain while Basil got his house in order. Here, most usurper wannabes wind up dead and you are left with John and Basil. Could be a recipe for bad civil war, but they choose to fight on different fronts (both know the age difference allows only one outcome). Basil was in OTL described to be someone who worked more for the Empire than for himself, and while that is certainly more hagiography than fact, some aspects of it are believable enough for me to think that he would not force the issue just for marginally more power.
3. Thus they have two good leaders on two fronts, who are actually linked by marriage.
Does this explain most of it?