It is significantly hard, so can you add something that allows for different modes (easy, medium, hard)
If you go into Scenario Options when starting a new game, then click the Edit AI Button, there is a slider to edit the AI income modifier, which changes how much money they get from factories and other sources of income.
If you set the modifier to 0.5, you can half their income, which should hopefully make the AI much easier to deal with.