If that bothers you, RPG is not the right genre for you maybe?
Completely stupid answer - if anything, RPG SHOULD be THE kind of game which put forward immersion and consistent world to begin with, due to its very nature.
As for variance in strength in humans, it wouldn't be a problem if not for the bad habit of making increase of power far too big - if you didn't double your health and damage every five levels, you wouldn't need to have all foes always around your own level.
