Could be just me, but this game is just way too hard. I just can't see anyone able to pull so many words out of thin air and type it all in at the same time.
To beat hard, i found myself not bothering carrying any soldier/weapon cards (except for thief) and just concentrate on mage/magic and builder/construction. This way, it increases the odds on you getting the cards you need.
It still requires a bit of luck but it's not that frustrating.
Needless to say, what cards you and the computer get at the beginning plays a big role in how well you do. If I don't get the mage/builder cards right a the beginning, I start trashing cards I can't use right away.
 "Mushroom Madness 2"){kind=icon}
 "Clockwords: Prelude"){kind=icon}
 "Castle Wars 2"){kind=icon}