[Phoenix-D]

" faced several times three enemy cruiser at once at the "easy level" setting, so in the expert level there will be a fleet of fifty enemy baseships??"

What the difficulty levels do is modable. In the stock game, as the difficulty goes up, the enemy gets -better- ships, not more of them. They get heavier (a destroyer will have 80% of its normal tonnage on Easy and 140% on Difficult), and they get better resistances.