The reason hit points are not a simulation is not because they are not granular. It's because they don't model anything. They are just a countdown clock.
Saving throws in classic D&D are likewise just a mode of plot armour, as Gygax explains in his DMG. 3E and 5e change this, taking them in a more simulationist direction with the well-known result that fighters go from being good at saving to being bad. With the Indomitable class ability being a further non-simulationist patch for this problem.
On surprise, I've got nothing to add to what @Hussar and I have already posted.
Every game has abstractions. Simulations do not recreate complex systems with 100% accuracy, a supercomputer could not perfectly model a realistic swordfight. I guarantee that SpaceX engineers ran a whole lot of simulations on the designs of their starship rockets and none of them predicted it would blow up on every test so far.
Granularity does not define whether or not something is a simulation. As far as what Gygax said, I still don't care.