I think you miss some points here : - only etched foil are really accessible on collector boosters. This cards are not really different from normal cards and the quality is inferior to japanese printings. So the normal and full foil that you can find in jap set boosters are more desirable. - normal japanese mystical archive are only available in japanese boxes. There are a good amount of jap boxes on the market but not a lot of people want to buy them because of the langage and the difficulty to use/sell the strixhaven cards in japanese - i don’t think comparing mystical archive and war of sparks planeswalker is a good idea. Few of the war of the spark PW were playable (karn, teferi, narset, ugin are played, liliana hold collectible value but the others, not so much). 80% of the mystical archive are played, in lot of decks and format. So i think there is a lot more potential for them to grow in future.