If I’m understanding your point correctly, the purpose for having all these rules is to provide something like an objective reality, so that not only can players know they can engage in horseback chases or mountainside carriage assaults, they’ll going to have a robust mechanism for doing it. I want that robustness without a large volume of rules, which is why I’m working on a robust conflict resolution process. So far, it’s been going well.
You make a lot of good points, and after work when I have time to write a lengthy post I'm going to have to address the board, but on this topic as a short response, I'd say "kinda".
My point is that well written "rules" serve the GM and that the GM's needs and games needs typically outstrip what can be done with a single system no matter how well designed. So, you want a robust conflict resolution system and yes that's a good basis for a game system. And that that conflict resolution system can be leveraged into different minigames is great, but often you need to structure each of those minigames slightly differently in order to get that "objective reality".
To give you a very concrete example, in Pendragon 5e the "Book of Battle" leverages the general tactical combat system to be the core part of a framework for the PC's participating in and influencing the outcome of mass combat by creating a minigame in which the PC's defeating individual enemies using the general tactical combat system has meaning and consequences within the larger fiction.
Now, you might not ever strictly need a mass combat system in any particular game. But any fantasy RPG benefits from it because every fantasy RPG is drawing from fantasy literature where mass combat is a major trope. Yes, it would be possible to replicate something like the "Book of Battle" combat system using just the basic rules, generous rulings, and fiat, but that's actually a major ask of the GM and likely to be a process that evolves a while before it gets truly robust.
And we could go further to say that for all the value of the "Book of Battle" it fails as a generic mass combat engine because it doesn't allow for PCs to take the role of commanders and influence the battle through strategic decision making as well as just tactical leadership. It has reasons for making that choice, and this doesn't mean it's bad rules, but it does leave a blank space for a GM to solve. Likewise, by it's own accounting the "Book of Battle" fails to resolve skirmishes that are two big to easily resolve using the tactical combat engine, but too small for its own assumptions and abstractions. So, there is another potential hole to fill.
I will say that I feel the "rules should be short and concise" party has gone off on a tangent where they are conflating lengthy with restrictive. And I think that those are tangential concepts where you can have either short or lengthy rules that are restrictive depending on how you write them. But proving that is a much longer conversation.
