Every time I play Civ5, it reminds me why I quit.
Exactly.
I don't think it can or will be fixed since what make it broken for me are really intentional. There are two design philosophies behind Civ V which makes it an anathema to me:
1) It's tuned for MP players.
MP players play to win. However, many SP players just play for fun and if the game is not fun they will just quit without caring a flying cricket about winning or losing.
By tuning for MP players (and the "serious" SP players who look for challenges from a game), it's necessary to remove all factors which can imbalance the game, like a very good wonder or a strong military unit. That, however, will rob the for-fun SP players of the cool targets that they can shoot for while playing the games. The game then just drags on with all the blah-blah following the blah-blah. Since they don't care about winning or losing or proving anything in the first place, the pain of going through the boredom to win is just not worth it.
2) It's gone way overboard in preventing the snowballing effect.
This is Syd Myer's design contention that it's important to keep the game "interesting" through out by preventing a snowballing effect of the initial advantages which makes the later part of the game a foregone conclusion.
Civ V goes way overboard on this. It seems every time I get too far ahead then the whole AI world would denounce me and refuse to deal with me for no apparent reason. And the global happiness system which sometimes plunges to below -30 for me after taking just a few cities (OK two of them are those big Gandhi cities which added around -25) without any quick way to recover from that. If I'm in the middle of a war, I don't want to sit around hitting the Return key for 20+ turns to fix the global happiness problem before attacking the next city. That might be OK for MP players, but for me it will be 20 turns of boredom and the only way to avoid that is to quit the game.
And then there are unintended consequences of the decision to adopt IUPT which makes the game drags on because everything becomes an oversized entity which takes dozens of turns to build. That adds to the feeling of "OK. Why am I going through all of these non-events when I can have more fun taking the puppy out for a walk ?"