The only arcomage I know of exept for this is the one you play in the old 3DO PC-games "Might And Magic", maybe that's the difference. Anyhow, I don't really know what more to say. A high cost card, maybe with a certain limit? - I do not think it's more powerful than many of the rare cards in this version of the game. It works perfectly well in MaM-Arcomage - but I might be wrong!
EDIT: I am so sorry. God, how stupid of me not to see my own mistake. Ofcourse I meant the WALL, not the TOWER. I thought there'd even be a card like that already existing, that's why I asked. Is there? And again, I am very sorry. So stupid!