I think that the "watcmaking" simulationist RPGs - the one I know best is Rolemaster - are especially trying to mechanically represent inputs into the given task.So if we are talking about "watchmaking" and people want to use the term "Simulationist" to mean "how many elements of a given task are represented in the mechanics." Then we are really talking about how well a given rule represents the action at hand. And oddly enough, the more details systems, like GURPS, don't get any closer to representing reality than fully narrative ones. They just have more rules to describe it.
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Oddly enough, for all their rules = they fail at simulating the real world effects.
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So what I was pointing out with Dune and Shadowdark is that some games get close to the mark, not by "watchmaking" but by paying attention to the results, the odds of results and the circumstances that create them.
As well, Dune show us that "simulation" does not start and end with Strength and ballistics penetration. It shows us that Simulation can apply to Politics, Intrigue and even large scale war.
But if we ARE just talking about "watchmaking" then, fine. I will shush.
A limitation that can arise is that they don't necessarily correlate that full spectrum of inputs into a "realistic" range of outputs. I mentioned Torchbearer upthread as a candidate modern simulationist RPG. It does take a lot of inputs - eg it has rules for random weather and how that factors into task difficulty - but relies more on table, and especially (but not exclusively) GM, judgement to determine exact results of attempted actions.
This is part of why I said it is good for details, colour, "proximity"-to-the-fiction sim. But not good for disclaiming decision-making. The "watchmaking" games tend to achieve the latter, even if the results they yield aren't always that realistic.