I think diplomacy needs overhauling. What's the point of having DI (training diplomats), to send them to said country, then to lose them and have to re-train new diplomats to talk to the same country again? It's stupid.
That's like sending a diplomat to a country, and when he comes back, executing him, and re-training another to take his place.

If anything, DI should be eliminated completely (like in HoI2), or, once you establish diplomatic relations with a country it should be permanent (no need to use further DI to contact the same nation again). That would be
far more realistic.
"Sir, your diplomat has just returned from Germany".
"Great. Now shoot him, and train another to take his place!"
"Err... yes sir."