Regarding the Hades pair, I think our strategy worked because we chose to focus upon more pressing areas (exploration, teching, wars with accessible AI, further exploration) until it was absolutely necessary to take on the barbs. And it turned out that it was not necessary (page 74, as
Duckweed acknowledges), although we had continued to plan for the possibility for some time (e.g. page 65,
Kossin outlines a fort chain that would have allowed us to travel through the north).
The benefits of Galleons could have been very limited, since we initially judged that we were playing on a Lakes map and knew that the AI capitals were all inland. Still, it quickly became clear that naval units would play some sort of role, and we believed it would be too slow/costly to rely upon Galleys moving from Mansa's western coast (huge maintenance fees if we'd settled a city there early; long revolt times, if we'd captured a Malinese city; no pop to whip or Forests to chop, if we'd settled there late). Had that role been limited solely to traveling around the southern mountain mass (on our continent, with the artificial Ocean by the Silver) then that would have been fine too. Discovering those Ocean tiles was the tipping point for me.
Engineering was clearly the crucial tech, and Astronomy is bulbed on the way to Engineering. I am not sure how much quicker it can be to bulb Compass, Machinery, and then self-tech Engineering, but I don't think it would make more than a few turns of difference. If all of your

comes through Caste specialists, you will pop numerous Great People regardless, and Compass/Optics/Astronomy, even if they do prove useless in and of themselves, are invaluable trade chips.
This was my first SGOTM so I'm not trying to claim credit for any of the above. It just represents my own reasoning and understanding of things.
Our teching was, incidentally, far from flawless.

In particular, we researched Drama before Currency (assuming the latter would become available through a trade). Guilds would have been a good post-Engineering pick, too. I think we underestimated our BPT rate, thanks to the numerous settled Great People strewn across the AI cities and remaining in Rep. Knights would have made the last few turns far less stressful.