^ Everything we see nowadays in Japan has been done (long) before in some form, be it visual kei (Ziggy Stardust) or Ladybeard (Dee Snider), to name a few.
From the seventies, a lot of rockbands started to make use of gimmicks to be more distinctive, like the above mentioned Kiss (makeup), Iron Maiden (Eddie) and ACDC (schoolboy outfit).
However, the few girls rockbands that gained popularity over the years (I can think of The Gogo's, The Runaways and The Bangles right now) were remarkably gimmick-less, probably because being all female was enough to stand out.
Right now in Japan we see an explosion of girls bands over the last decade. Maybe Bandmaid feel the same urge to stand out just as male rockbands did (and still do) in the west, just like a lot of idol groups have some sort of gimmick to stand out from the crowd, with Passpo being a prime example.