The very base of it is the simple "You select a dialogue option > NPC reacts to dialogue option" which is still a system.
I think I am diving into an unnecessary argument, but here is where I have a problem. Because that's not how dialogues work - NPCs don't "react" to the option you pick, because there is no system that governs what it is that you said and what are NPCs as a response (aside perhaps from
Arcanum. It's all hand desined "if you pick option A that leads to node B3". I have very shallow understranding, but from what I understand if you were able to ask lets say any NPC about a location, and there was a system that would check the knowledge of that NPC and respond accordingly - that would be system. Designer hand writing the question in a conversation node, handwiritng the response in another node and manually linking them together is scripting. (to explain myself further here is another Tim Cain
video on programing and scripting - this is what put my thinking on that lane).
You can boil down combat into similar terms if you try hard enough. It's all just "Use Attack on Man" and then the opposing response of "Man uses attack on you" - The depth of the system comes in the form of the options presented, how the target reacts to those options, how options build off of statistics... Not unlike dialogues.
Well, no. I think an example of what I would call "scripted" combat would be Disco Elysium's shootout, or Pillars of Eternity/Pathfinders story book moments. Those are narratively combat/stealth events, but they aren't using actual combat/stealth systems - just hand written text nodes, using hand made conversation trees and embedded checks to govern out progression through that conversation tree.
Combat system has rules - if you attack NPC they become hostile, AI turns on and you attack each other in turns until one of you dies - a regular verbs, and responses that work consistantly and in every encounter. A change to the system affects all encounters (which I would assume is what makes it easier to invest into enhancing complexity of combat, than conversations where each individual conversation requires to be made from scratch).
And yes, there has been attempt (especially by Obsidian) to add more systemic elements to their conversation trees. But those also often don't turn out so well. While PoE Disposition system was great, Deadfire's companion relationship was quite a
misfire. Even in a mechanically simple implementation of reputation system as BG3, companions to sometimes miss the context of the action. I wouldn't go as far as to say that humans are too complex for other humans to believably reduce them to a game system, but at least a game should probably put more focus on it to get it right. (Hey Josh uses "hand scripting" to discribe dialogue reactivity, so maybe I am unto something here afterall!)