"Mounted warriors are as useless as horsemen against pikemen." If mounted warriors are useless against pikemen, horsemen are useless against spearmen! They aren't as great as samurai, but they are cheap. And the rider is better than samurai, but Japan is a better civ than China because it is religious. In your next game, save up a few dozen horsemen and upgrade them to riders. You will take out 2 average civs or 1 huge civ with this. The samurai last longer than riders, but the rider's short term benefit will set you up for the win. I still prefer Japan, but China is also an excellent civ when you need the 3 movement to hold a huge empire together. Because resources like horses are more rare in smaller maps, Japan would have an advantage with their UU. China's UU would be better suited for a large map. Ironically, I think China's traits would suit it for a small map. Like the other Asian civs, China can be very effective early in the game or later in the game.