A while back I moved from Immortal to Deity, and I've more-or-less gotten the hang of the higher difficulty by now. I can get Scientific, cultural, or diplomatic victories, I can usually win defensive wars, and occasionally I can wage a successful offensive war.
But you don't win a Domination victory by waging one or two successful offensive wars; you have to wage (and win) 7 successful wars. I'm just not seeing how it's theoretically possible. Whenever I deviate from the "optimum" science path to pick up (and build war-related stuff, that's when I fall behind. So an army is good for conquering one, maybe two civs, and then I have to scramble to catch up in research, army upgrades, etc. If I'm doing really well, I'll catch up & be able to take out another 1 or 2 AIs... and after that conquest is flat-out impossible. I don't see how you can deal with an AI with (for example) 10 cities, each of which is supporting 6 or 7 units, thus creating a ridiculous carpet that they can resupply faster than you can kill them.
Basically, I'm not getting what you folks are doing mid-game. How do you possibly detour into war-stuff (both tech research & what your cities construct) and yet remain competitive with technology & money?
It is possible to win 7 wars but not on every map. I have started from getting only Spaceship deity victories to trying out Dom. deity victories. I have won a fair number of DomV games on fair maps but on others I just find it impossible to do so.
As for late game AIs with 10-20 cities(eg late game Attila) you have to spam a lot of artillery along with cavalry and 1/2 AA guns. I have followed peddroelms 2-city honor strategy but I just cannot implement his full honor approach. I mostly tend for liberty-comm trees.
Anyway my war throghout the ages approach has been a 2-3 city full liberty opener. Cap BO scout/monument/scout/gran/archers(a settler if another lux heavy location is present). I personally find that it is important to not try to build too many settlers and not have any archers.I try to steal about 2 workers. If I have a DoF I build 8 archers otherwise I stick with 5. Expo is settled near luxes and I directly go for mon./library in expo. Then if I have found an AI to Dow I go for construction,otherwise philo. Archers are upgraded to CB and sent on quest/CS exp. Now I usually hard build the NC if I am not gong for a CB rush against one AI. If I am going for CB rush then the cap builds more archers/CB and the NC is finished with GE(GS is probably better from Lib finisher. I do not know the maths). Also I tend to get horsemen unlocked quite quickly. I also try to get a caravan up(cannot afford to build it always) and tend to beeline machinery. Meanwhile excess luxes are sold(can be done by keeping the expo at low pop).
The ideal army by the end of machinery(about t90-110) is 10-12 XB,1-2 Horseman. This army is enough to get you atleast 2 caps(probably 3 as I am a very poor warmonger) of any civ by t150. In the meantime after the army is built I go for markets. I also beeline education after machinery. After markets I build univ. and beeline artillery. In games where I get more than 3/4 caps by t140 I just stop building buildings and just get XBs to finish the game. Otherwise I tend for Oxford and try for artillery(can be reached at t180-190 with about 120-150 beakers and oxford). It is important to note that a too early artillery is not needed. Rather try to build as many cannons(8-9) as possible and then use oxford for the arty and upgrade the cannons. At t190 you should have an army of atleast 12 arty and 2 musket along with your XB army(some of whom will have range and logistics.)
12-18 arty(you cannot have enough of them) and a knight/cavalry will take down 2 civs by t225-t230.(thus bringing the total to 4-5 dead civs) In the meantime I try to go for Industrialization/Modern era depending on my gold/production. If the AI does not have flight you can usually win by t260-t270 with just arty and cav. You can also go for landships/tanks. It is when AI has flight the game becomes extremely difficult and I do not know what to do.
As for economy markets and banks can help you from getting off the red. I usually do not have the time for banks though.
Social policy is full lib+full comm+ 2 rat(if I have culture) and mostly order(happiness from monuments.)
The thing is that XBs and arty are units that have great longevity and even if the AI has outteched you you can use them to beat the AIs. The counter of XBs are stronger melee units and the counter for arty is flight.
For technically winning DomV you can play for SV and then build tonnes of Stealth and XCOM+nukes to win. However you have to do it quickly before AI launches spaceship.
P.S. Water map deity domination are a different thing altogether and is very easy. Just keep on building frigates and then Battleships. In-fact you can just beeline frigates and battleships for water maps.