There is a big difference IMO. Characters aren't restocked very often and it makes more sense, because you want the Characters dead dead (ie in the grave).
The Crawler is designed to have many options to restock cards and return them to hand.
True, but with the Crawler grave you have choice, and you can choose to hold out until you complete that Quest and then start retrieving magic cards - pull them early and you'll have to wait longer to complete the Quest.
Another issue is that once you get close you could just discard Magic cards to complete the quest.
Another possible angle might be to make a Magic card that cost 7 or 8 Resources. Call it Megiddo or something equally appropriate. It would presumably be a damage card that really fried the bad guys.
Then Archmage's condition could simply be "Play Megiddo".