What the OP is talking about, which is valid, is that diplomacy trading is extremely easy. It has no level of sophistication from GC2 and is very simple to "cheese" in the player's favor. GC3 Diplomacy is underwhelming and is advanced as a game from the 1990s.
Want an AI to go to war? Just give them a bunch of low level tech, Exploration Treaty and some other forms of "Diplomatic Treaty" and they will go to war with a "Trusted" AI even if they are vastly outclassed.
Want to wipe out another AI's treasury? Just give them Exploration Treaty and you have thousands of credits while bankrupting the AI.
Behind on Tech? Just throw 10 Duranthium and a "Diplomatic Treaty" and you can catch up instantly.
The point is, the treaties are bull and the AI too easily accepts trade offers. The player has no real incentive to invest in diplomacy tech since you can get what you want with vapid treaty offers anyhow. The treaties that "offer" something to the AI should come at a cost to the owner. If a player uses Slave Brokering, it should cost the player something to give bonuses to the recipient. The level of trust that an AI has towards another faction should far outweigh (unless you are very advanced in diplomacy) anything that a player can offer in trade-for-war. There aren't any worthwhile trade treaties either (trade is a joke as well) and not much to do if the player turns off Tech Brokering. It is just a waste of a mechanic.
Diplomacy as a whole needs an entire rework. It just didn't bring anything worthwhile to the game and can't hold a candle to the more advanced strategy titles out at the moment.
Hopefully the dev team has ideas for this mechanic since it doesn't take much effort to play other acclaimed titles and see that this is something that is sorely missing in the GC series.