I don't doubt that this information is true. The problem is that all of the stuff that determines diplomacy is completely undocumented, and never explained at any point in time, anywhere in-game. You are never told the rules of the game. Figuring out the diplomatic system in Civ5 requires a process of tedious trial and error (reverse-engineering what works and what doesn't work over the process of many games) and/or reading the actual programming code itself in the XML files. With enough time and repetition, yeah, sure, you can figure out how to manipulate things. This is a computer AI, after all - it will behave according to predictable patterns.
But that doesn't change the fact that diplomacy is based on undocumented, arcane rules that are never explained at any point in time. Should players really be expected to go to those lengths in order to understand why the AI is acting the way it does? When you need to consult XML charts and an undocumented, never-diplayed "OPINION" rating?
It feels like a rather poor system to me.