Well, look at "Bad Luck" the example Aspect. This sure as hell isn't worse than that. And, because of the Duration Factor, making it last any reasonable length of time IS much harder than a Mild Consequence
I am pretty sure that whatever Archmage_Cowl is planning is worse than "Bad Luck". Really if something on the level of Bad Luck is the worst "death curse" that he can land on someone, well that is just sad, unless it lasts for a decade or something.
Really the key point then is that Archmage_Cowl needs to make sure whatever the result of the curse is that it is not worse than a maneuver would allow. If it is then a consequence should be used. This is entirely a GM and player call....
Pg. 265
A mild curse might place an aspect on a target, but once the magic runs its course, the victim is left largely as he was. In contrast, a spell that burns out a victim’s emotional capacity may also last for months, but not because there’s any magic left behind. Players and GMs should keep this dividing line in mind when deciding whether to express a spell’s effect as a temporary aspect (like a maneuver) versus a consequence or permanent change.
The real problem as I see it is that a mild consequence for one person might cost 10+4+2 = 16, and would last only once scene after recovery starts, which means it could easily be resolved in a day or less. Meanwhile "Bad Luck" with 16 shifts lasts "A few days". A moderate consequence (18) would likely last until the end of the next session, which is less than the "A few weeks" that Bad Luck would last for that cost. Same with Severe, it lasts until the end of the next scenario vs "A few months" for the same cost, but then you can keep going with Bad Luck right up to a decade or more.... And since you can do things like Blindness, Fear of clothing, Fear of people, endless laughter, Deaf, Dumb (devastating to a wizard), etc., and there is NO method for removing such a curse, maneuver curses are potentially just way over-powered.