I'm wondering if the real message here is that, while the three styles are different and have different (exclusive) goals, the synergy between the differing styles creates the complexity we're all familiar with.
It depends whose message. The
original threefold model which Edwards greatly distorted was much more inclusive. He also misused a lot of concepts found in Everway.
On the surface, the goals appear exclusive but in application, even ardent Forge theory supporters can't agree on what's exactly going on. To the point where several (including Ron Edwards himself) wonder if "simulationism" even exists.
ADnD allows you to play a paladin. He kicks ass because he's pretty much like a fighter
and he's got cool powers on top of that. However, he's a holy dude. He has to be lawful good. He can't keep excess wealth, he's got restrictions on who he will associate with, what he can do and so on.
Agenda:
A) Gamist
Is the game trying to balance out the cool powers the paladin gets over the fighter with a set of restrictions? Is a player opting for the paladin class looking for a challenge, where you play an adventurer who is really a more potent fighter and do as well as you can despite the additional restrictions?
B) Simulationist
Is paladin really just an implicit DnD default assumption? In the default environment of the game, it's just cool that there are holy warriors and it makes sense that they have powers and it makes sense that they also have a paladin "code" of sorts. It doesn't really make any sense to be this paragon of virtue and not have a code. Could a player be wondering what it's like to play such a character, explore what the implications are in the environment?
C) Narrativist
Is the Paladin code a strong premise for fantasy adventuring? Did the game as written offer a strong story-driving mechanic? For some players, could it be all about the drama and moral implications of adventuring under such a code?
D) Common sense
Could it be about any combination of those things, plus many more motivations and implications?
Note how the three agendas intersect. Note how, as is usually the case even with Forge theorists, simulationism and narrativism blur into each other so much it's often useless to talk in these terms.
You take any DnD concept and distill it and you're likely to get a mix of things. I think the synergy you speak of is present not only in style but also in goals, if that makes sense.