There HAS to be a secret boss in ch6

Even though we have all the shadow crystals needed to make the 'special thing' Seam said they could make for us. I really believe (and hope) that there will be a secret boss in some form.

From a gameplay standpoint, I think that not having a secret boss would take away the mystery of finding the boss along with the gameplay of the fight. And from a lore perspective it takes away the opportunity to give spotlight characters like ERAM, FRIEND, the Knight, or even a not yet known character.

(Considering there's a theory that says FRIEND will be the main boss, a diffent character would be a nice surprise)

About the purpose of the secret boss, rather than giving us a crystal, it could maybe provide a key item of sorts for a chapter 7 secret or something like that.

TLDR: Not having a secret boss would probably make ch6 feel more empty and waste both a chance to get lore and a good fight. And the fight can also serve a purpose even though we have all crystals.