It's impossible to play on Hard

[aghiuta]

You could try using the Army shop mod from the russian forum. You have to pay double the price for the troops but I think it is a fair deal.
I am currently using a summoning army: royal griffins (with 2 phantom spells in first turn due to lvl 2 higher magic), royal thorns, dryads (from song of the wind scroll), demonologists and red dragons.
In first turn my initial 5 stacks army becomes a 13 stacks army with the added 2 stacks of phantom royal griffins, 3 stacks of summoned heavenly guards, 2 stakcs of summoned thorns and 1 demon stack.
This way I have a lot of tanks and the griffins and the demons are furious so always retaliating.
Now I can win lethal fights with no or minimal losses.