After playing a few times I could beat deity, emperor --> immortal shouldn't be too bad.
The way barbs are tuned it's hard to justify anything other than getting out some slingers --> archers ASAP. Those archers can wipe barbs (sometimes it is completely impossible to block scouts causing spawns, and AIs can spawn barbs that attack you which is broken), but they also double as city-state murderers, anti-AI rush, and rushing the AI yourself.
So already the opening is pretty well set down. Triple (or more) slinger into archers is overwhelmingly favorable. From there you expand and get commercial hubs/improvements/some campuses/later industrial districts down, killing AI if you have any to kill because that's more favorable than playing nice, consistently.
Ranged spam with mounted is probably the way to go in principle, but I didn't have any trouble just spamming melee + occasional mounted with battering rams on a deity Pangaea domination with Norway, so you have a lot of leeway with wars.
If you still have some around battering rams and siege engines even work with mechanized infantry...