After the exploration phase (the scout unit is the only unit with the right/useful early promotions) + planning your 4-5 cities the game will become very boring and repetitive.The game is fun at the very beginning...
There's absolute no hope this will change in the future and yes the AI gets at all levels a 40% happiness discount.the AI is really terrible, they just cheat.
I've played several games at Emperor level and gave the AI the same level of happiness as the human player, it opened my eyes to see the horrible game design of civ5.
Expansion (vertical + horizontal), research and economy are tied to the happiness mechanic, while the AI can't handle combat because of 1 upt.
Both game mechanics are failing miserably.
No patch or DLC can save this civ version if those 2 game mechanics don't change.