Wow you are making deity look easy.
To be fair, it is really the map that makes it look easy. I knew the start would be good, but I couldn't anticipate that the rest of the map also would play so much in my favor. Freddy was the only AI with somewhat decent room to expand without chopping tons of jungle, all the other had quite tough starts. Especially my nearest neighbors and Charly+Monty. Hannibal had a bit more space before running into jungle, but still less space than I had.
Also, I don't know what's up with them avoiding settling on hills. Rammy had one hill city, Freddy also has only one and Washington has two. This will make conquering them so much easier!
Random thoughts:
-I don't think much is gained from Theo bulb + Paper Oracle vs Theo Oracle + Paper bulb. The Oracle date should be safer taking Theo and it's easier to get scientist GPP than priest GPP. Either way you will be dealing with some GPP pollution if you run scientists in your Oracle city.
This is probably true. The only small benefit of this would be that those GP points are coming in sooner and the first GP is generated passively without the need of running specialists and diverting any population from working the good tiles we want to work early. In this game I just had time to get up a library in Istanbul and grow to size 6 by the time the prophet was born and I had to start running scientists. On the other hand, if oracling theo, then we can skip med and masonry and don't need hammers for SH, which could mean faster expansion and faster libraries. With scientists running early in 2 cities, I'm sure it is possible to get 3 GScientists by 600BC for paper+edu bulb. Then there is of course the GP pool polluting that you mention...
-Janissary odds vs LBs actually don't look too much worse than Cuirs here although this is with Cover promo and i don't think you will always get matchups vs LBs if you use Cover on many units. Still, 9.9 vs 8.1 isn't bad since i believe a Combat II Cuir here would be 14.4 vs 11.1 albeit with the extra WD chance and the 1st strike immunity. This gets you something like a 600-800 year head start though with slower units and perhaps a little less sustainability.
That longbow was upgraded from archer the same turn and didn't have any fortification bonus. With the 25% fortification bonus it becomes 9.9 vs 9.6 (58%), which is okay, but not exactly crushing. Make it 60% cultural defenses and the odds drop to 27%, put 40% cultural defense on a hill and we are at 19% and with 60% cultural defense in hill city we are down to 9%. This is with C1+cover on our guy. In non hill cities these will instead face maces if such are available as defenders.
It is nice though that the AI won't have pinch available for a long time. Instead they keep giving shock promotions to their maces, which are totally useless against my guys.
All 3 of those cities he has left on the mainland are worth taking if possible. Leave him with the the stuff on the other continent and there will never be any issues with cities revolting. All are also coastal for GLH trade routes, and that should give you like 8 coastal cities in total.
Can the AP force me to give his cities back if he has no more cities on this continent?
Well I didn't want to be a damper on the time and effort put into this post, but........
My personal experience is that Janis' really suck by themselves. I'd much rather use this opening to beeline towards Machinery and Engineering. I think it would yield much better results.
hmm interesting game

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I will only touch on the problem with strategy being viable on deity confirming it's value.
the biggest problem here is that on lower difficulties (emperor and lower) there are much quicker other strategies... being chariot rush, axe rush and mostly ofc HA rush...
if you would play this start on emperor and have horses at this point of game probably 2-3 AI's would be dead
I'm sure you both are right. In terms of winning as soon as possible there are better strategies. However, this is a game and to me the value of a game is determined by how much enjoyment I get from it. The part I enjoy the most is figuring out new things to do, trying alternative approaches and exploring all the different options. Redoing the same path I've done a ton of times before quickly bores me. That's why I rather do a Janissary rush or Cataphract rush than a HA rush. Other people might get more enjoyment from trying to refine available strategies to optimize results, for them a Janissary rush is probably not worth considering.