I think they are a good balance. Ive been using scaredgirls unupped FG deck, and been able to usually beat them, although occasionally they beat me. I say they are a real good difficulty, because just because you can beat a level 3 doesnt mean you can beat a lvl 5, trust me on that, i learned that the hard way when I first started playing. I think it is a good stepping stone for the fgs, and instead of making them harder, i think it would be a better idea to make a new lvl 6 ai that follows the same rules, but has better decks (and not randomized ones), but not quite as powerful as the FGs, that way we have the lvl 3s, the ai that are weaker than the fgs, but stronger than the lvl 3s and leaning more towards the lvl 3 side, then the level 6s that will be stronger than lvl 3 and weaker than the fgs, but leaning more towards the fgs. Maybe a pure upgraded deck (but have it so that you can only win upgraded cards still a certain % and the rest will be defaulted to a non upgraded/