"When talking is permitted, doesn't that really take the challenge away from the art of Diplomacy? I mean, you can say ANYTHING you want."
Yes, and that, along with the fact that everybody else can too, is exactly where the challenge comes from.
I guess maybe it's your experience in life that, as long as you're allowed to talk, you can easily convince anybody of anything, and they'll do whatever you say. But that is not my experience, and I find there is quite a lot of craft and challenge in verbally negotiating, convincing, and working together.
Regardless, if you prefer Gunboat, fine and good, but don't claim it's "purest diplomacy." THAT, unlike which game is better, is a demonstrably false and inane claim.