I think we're going to stick with multiclass level being determined from the level where you first gained a move from that class.
Thank you for considering my position on this. If you do decide to keep this mechanic, please consider putting something in the move text that appears on the character sheets, so the importance of taking casting multiclasses as early as possible is obvious, and not hidden in a rulebook that is otherwise rarely necessary to look at for character creation and advancement. As it is, the only reference to levels could suggest that the move acts as though you are one lower level, which is not the case for spellcasting.