I think any system that broadly gives the impression of mimicking the environment, world, events we're trying to to evoke can be considered a simulation.
The flow of events is what we are simulating. It's how our PCs interact with and respond to a fictional magical world.
As with
@Hussar's post upthread, this means that 4e D&D's Come and Get It counts as, or is a part of, a simulation: the fighter performs some sort of manoeuvre using their weapon, as a result of which their opponents end up closer to them, and get beaten up. This absolutely gives the impression of mimicking the environment and the events we're trying to evoke in our play!
A technical definition of simulation can be found
here "
A simulation is a model that mimics the operation of an existing or proposed system, providing evidence for decision-making by being able to test different scenarios or process changes." Another relevant sentence "
Any system or process that has a flow of events can be simulated."
This technical definition is not the same as what I've quoted just above. Obviously, combat is a process that has a flow of events, and hence can be simulated; but no version of D&D mimics the operation of that process, nor provides evidence for decision-making by testing scenarios. In D&D we don't make decisions based on modelling the process: we make decisions by actually participating in a gameplay process (that involves rolling dice, adjusting hit point tallies, perhaps tracking position on a board, etc). We don't
simulate playing the game - we actually
play the game.
As far as dragons, the fiction for dragons in D&D is limited to the rules of the game. Dragon lore varies so widely there has to be some baseline.
Here, I agree with
@Campbell. If we're establishing the fiction
by reading it off the game rules, then whatever those rules might be, they're not a
simulation of anything. Because the supposed "thing" - the fiction - is not establishing any parameters against which we measure the adequacy of the rules outcomes.
Are high level PCs in D&D supremely good at what they do? Even exceeding normal (real world) human capabilities? Sure. That's part of what we're simulating, a world where the best of the best can indeed face down dragons. At times it's a very crude simulation, one that has many simplifications and limitations because it's a TTRPG.
We aren't attempting to simulate training for the Olympics. Being really, really good at fighting doesn't mean you suddenly know how to pole vault. You have a bit of an edge if it's something you have training in because your proficiency bonus goes up. Your long jump increases if you've been pumping iron and are stronger.
This particular bit makes no sense to me, for different reasons: whatever is involved in a person getting better at
hand-to-hand fighting will also make them faster, stronger etc in general, such that they are better at jumping, and perhaps also at pole vaulting (although the latter does use a more specific skill set). You can't be strong and fast enough to stand against a dragon, for instance, without also being strong and fast enough to pull of other amazing athletic feats (like throwing things long distances, pushing over heavy objects, lifting great weights, jumping far, etc).
The 5e Basic Rules (p 71) say that "you can move through a hostile creature’s space only if the creature is at least two sizes larger or smaller than you." A Bugbear is classified as Medium, STR 15, 27 hp; an Ogre as Large, STR 19, 59 hp; a Young Red Dragon as Large, STR 23, 178 hp (cf a crocodile which is Large, STR 15, 19 hp). What stops the Ogre or the Dragon from just pushing past a human warrior, as a bear or elephant would?
this is just an outlier effect of simplified rules that doesn't really affect 99% of combats. In addition, no fighter can shove a dragon without magic or some supernatural ability. You can't normally shove someone more than 1 size larger than your PC.
The ability of a human warrior to stop an Ogre or dragon just pushing past them comes up a fair bit in D&D melee combat, I think. And how does a fighter shove an Ogre, or a Young Red Dragon? If they're strong and/or fast enough to do that, they're pretty athletic!
Also, p 73 of the Basic Rules tells us that "[o]n a hit, an unarmed strike deals bludgeoning damage equal to 1 + your Strength modifier." For a 20 STR fighter, that's 6 hp. So a 20th level fighter can punch a crocodile to death in one round of combat. That's a pretty strong person! Wouldn't they be able to push over cars, punch down doors, even knock over small houses, etc?
EDIT: A BattleMaster can use superiority dice and manoeuvres to push the Ogre 15 feet away! And adding d8 superiority dice to damage means that an 18 STR fighter can kill the crocodile with two punches (2*(1+4) + 2d8 =, on average, 19 hp of damage). So a 5th level fighter can pull off this superhuman feat!