Is size actually a concern in the modern world? With transmission and storage size is practically a nonissue and we have proper rather cheap compression anyway. And in memory? We have gigabytes of ram, who cares? Of the potential situations where it may become an issue that I can think of, pretty much none of them are on end user hardware.
the other way round, having a wildly variable size depending on the character can be a weakness. In japanese EUC was sometime used despite its shortcomings to force 16bit by character.
