I like the idea of making pacts. Diplomacy is something that I think a lot of people clamor for. It's wildly popular in Civ VI.
I don't want just a hack and slash game. If I want that, Medieval II: Total War is still downloadable and playable. Heck, Lords of the Realm II is still out there.
The problem with KoH 1, which I think we've beaten to death, is that diplomacy was done so poorly.
So yes please, invest more in diplomacy. It makes the world a much more living, breathing entity.
Different personalities, different means to the end. This ruler prefers alliances. This one is the lone wolf. That one can't be trusted, this other one can. He wants to use spies to take over kingdoms, that one believes in economic warfare.
The more varied, the more diplomacy can play a role. Hack and slash should be but one avenue to victory.