The RGFA model is more of a "approach to play". It's how you decide "what happens" when you have to make a decision.
If you think "what would make for the best story", dramatist. Note, dramatist GMs often have a particular story they want to tell already in their mind, while narrativist GMs are supposed to let the story emerge naturally and only facilitate it. Hence the different approach to techniques like fudging and illusionism, which narrativists often consider "robbing players of real contribution to the story". And so do I
If you think "what would really happen in this game world, given these circumstances (and what edge cases are possible given extremely unlikely results of the dice)", you're a simualtionist. Welcome to the club
If you think "what would make for a fair challenge", it's the gamist logic. Mind you, a "fair challenge" isn't always one that you can fight directly!
But we get into "combat as sport" and "combat as war" here, and this is completely unrelated to playstyles.
"dramatist": is the style which values how well the in-game action creates a satisfying storyline. Different kinds of stories may be viewed as satisfying, depending on individual tastes, varying from fanciful pulp action to believable character drama. It is the end result of the story which is important.
"gamist": is the style which values setting up a fair challenge for the players (as opposed to the PCs). The challenges may be tactical combat, intellectual mysteries, politics, or anything else. The players will try to solve the problems they are presented with, and in turn the GM will make these challenges solvable if they act intelligently within the contract.
"simulationist": is the style which values resolving in-game events based solely on game-world considerations, without allowing any meta-game concerns to affect the decision. Thus, a fully simulationist GM will not fudge results to save PCs or to save her plot, or even change facts unknown to the players. Such a GM may use meta-game considerations to decide meta-game issues like who is playing which character, whether to play out a conversation word for word, and so forth, but she will resolve actual in-game events based on what would "really" happen.
A pure dramatist might run a gritty, low-key drama where the PCs are true-to-life characters who perhaps concentrate on their work. In this case, the dramatic story might be framed around how they relate to each other and the tension produced. Dramatist campaigns also include comedic campaigns, where the in-game action is tailored for humorous effect rather than classical "drama". The key is that in-game events are tailored based on how satisfying the storyline of the campaign is.
A gamist could run a mystery game where the PCs are challenged to find the killer based not just on physical clues, but also on the personalities and motivations of the suspects. Note that this is similar on the surface to a dramatic story, but the emphasis is on making it solvable yet challenging to the players. A purely dramatist mystery might make a better story, but a purely gamist mystery will be a fairer test of the player's wits.
Simulationism by definition is going to try to be "realistic" within the game-world, although it may have natural laws different than the real world. However, the players are not neccessarily obsessed with rules or physics. A simulationist game could just as well focus on political discussion between important figures, or rebels fighting a propaganda war to win over the masses.
A purely simulationist mystery would start with determining how the crime was carried out based only on in-game factors. The logical consequences of this might mean that the players can solve it easily, or that they can't solve it at all, or that they can only solve it by turning it over other authorities. An absolutely pure simulationist GM won't go back and change things to make the mystery work better for the PCs.
OTOH, the GSN has a bit different ideas. Most of all, it's defined as a "goal of play", what you want the game to produce.
Here's a working definition for comparison.
Gamism is expressed by competition among participants (the real people); it includes victory and loss conditions for characters, both short-term and long-term, that reflect on the people's actual play strategies. The listed elements provide an arena for the competition.
Simulationism is expressed by enhancing one or more of the listed elements in Set 1 above; in other words, Simulationism heightens and focuses Exploration as the priority of play. The players may be greatly concerned with the internal logic and experiential consistency of that Exploration.
Narrativism is expressed by the creation, via role-playing, of a story with a recognizable theme. The characters are formal protagonists in the classic Lit 101 sense, and the players are often considered co-authors. The listed elements provide the material for narrative conflict (again, in the specialized sense of literary analysis).Link
for both definitions I used.