You have to move part of the fleet away from Japan to pull off all your objectives, and your land forces in China are spread thin.
If you invest in factories, transports, and non-naval units, USA is more powerful than you on the SZ 6 side of the board and can step right up to you, taking Iwo and forcing you to either head back home to defend (losing the chance to take india or spice) or potentially lose control of the SZ 6 and 19 for a while.
Once the US is squatting on you (recall that you can land planes in Russia early during a J1), your choices become limited, Japan can’t really demolish and focus on USSR or China during a J1 and USA gets max income, asap. The focus in most J1 is on UK India, but the arrangement of transports at game start limits you to moving south or moving home, so you cant get the numbers or income for the long game.