The dresses have sufficient variation in their patterns and flourishes to justify separate costumes in my eyes (not to mention the fact that they're mostly seperate classes, with only Ceada and Cordelia sharing a moveset). Besides, would Xander, Ryoma, and Chrom be in the same outfit and vest or would they be wearing something besides swim trunks since Frederick would already have them? Who gets the 50s stripped onsie?