Wanna know why do i think diplomacy is screwed?
I was playing Venice, m/m. Destroyed Milan, had those rich islands, jerusalem also. Then a french princess purposed marriage. I tough "cool :), these marriages sound like stable aliances." My prince was married, Venice and french bounded for ever. Next turn a royal member of the french faction, with some peasants and other stupid units sieged one of my well defended towns. Our relations were at the best level, we had a marriage aliance and the AI just attacked me in the very next turn.
Now you tell me that diplomacy is working and the AI isnt ridiculous!