So when Bismarck asks me to stop purchasing land near his cities and I assure him that it won't happen again, yet I do it again within a couple of turns and he immediately comes back saying how disappointed he is that I did that, and 10 or so turns later he declares war, that is non-existent diplomacy?
Yes, it is non-existent diplomacy.
Do you know how LONG you're bound to such an agreement?
Do you know whether this includes the cultural extension, too?
Do you know whether this pact is influenced by him, Bismarck, found a new city even closer to your borders?
I have to admit, I don't know any of these things. Which actually renders all possible repliese meaningless, if not in raising the chance of getting attacked to even a higher level ("We settle where we want").
Look, I can understand if the seemingly erratic behaviour of AIs and the lack (most of the time) of tangible feedback to the player with their diplomatic interactions can be frustrating, but I think you're kidding yourself in denying that diplomacy exists in the game, or just intentionally exaggerating to make your point.
Actually, I think YOU are kidding yourself.
You want the diplomacy to be meaningful in a certain way. Yet, as long as there isn't any meaningful, understandable feedback, it comes down to some kind of multiple choice.
Pick whatever option pleases you, and still you don't know about the results.
When my people are incredibly unhappy, I've had leaders approach me saying they can hear the screams and cries of the people living under my rule. I get the impression that AIs take into account various factors that weren't used in civ4. The happiness of my population is just one example.
Yes, and when you and say Askia are already at war against say Gandhi, Askia comes later and asks about a pact of secrecy against Gandhi.
Now, how meaningful is this?
Obviously, this request at that moment isn't meaningful in any way. So, what are the consequences of the option which you will pick?
Are there any consequences at all?
You don't know it. I don't know it, either.
When in diplomacy, you are just in a black box and don't get any feedback. Which means, there isn't any "diplomacy" at all.