Enemy are scaled by difficulty lvl, so if it`s to hard try lower ( you didnt say are you playing on normal/hard/impossible).
And when you get highest lvl you`re units will have same bonuses as enemy, only depending how lucky you were in lvlingup and getting useful bonuses. As you play with items,skills,spells,pet dragon, it`s expected to play vs stronger opponents to be at least a bit interesting.
I advertised one great mod for the Legend ( version for AP/CW is in work i think), there enemy heroes have same(or higher bonuses) then you with skills,enemy mage heroes have double/triple spell cast/turn and mana regen 10% of mana pool/turn, warrior heroes lower your units physical resistances, or speed/initiative in first two turn etc. Mana/rage goes to 0 after 15/20 turns , great skills changes, great kid bonuses form wives (2 new wife available). . . Who want to have some fun with old-new version of KB the Legend check this out :
http://forum.1cpublishing.eu/showthread.php?t=29080