User blog comment:LucidPigeons/Category Cleanup/@comment-26205772-20160301150817/@comment-1969141-20160305163240

Alternate/True Forms AND splitting the alternate form were originally meant to avoid another problem. For instance, users kept adding the category "Dragons" to Maleficent, but it did not do since she transforms into one but is not one. Also, it was meant for villains whose transformation was considered in-universe as a distinct character,  for instance Dry Bowser or Safer Sephiroth.

Whether this is relevant or not is another debate though.

Also, there is a distinction between a character that can transform at will, and a character that unleashes their "true form"