I don't think you can compare it to PvP games, because even if you improve constantly, you still could be in the lowest rank if majority of players improve faster than you. Besides, those are weird rank distributions. SC2 makes much more sense that a mediocre player is in the mediocre rank: https://www.rankedftw.com/stats/leagues/1v1/#v=2&r=-2&sx=a Still, it doesn't prove anything, because it's matter of algorithm that determine which rank you should be in and it differs. I am curious specially about difficulty per hour for single player games. You don't need to seek guides or tips on forum to improve. It does happen when you play anyway and if you play enough time, the lowest difficulty will become too easy. But then again, it also depends how difficulty levels are designed.