Abstraction, is the font of realism.
For D&D this perfectly suitable and true. Better armor is more effective, more skilled people are harder to kill (more HP) , better weapons are better at killing, combat is sometimes random.
Its not a reality simulation but it provides perfectly playable results that are not that far off from the haphazard nature of a real fight.
This is why I think that despite tons of excellent more "realistic" systems D&D endures. Its good enough and its fun, and thats plenty.