The problem is that while 18 is the most powerful female character, she's not very important . She had a lot of potential (she kicked Vegeta's ass when she first showed up!), but Toriyama just had her sit idly by on the sidelines, stoic and nonchalant, not doing as much as the other girlfriends/wives (
Toei tried to make her more useful, but there's only so much they could do). ...