Head-canon is accepted as canon, regardless of the state of evidence. Could have backing, might not.Well, head-canon is fanfiction. I have my head-canon for unexplained elements, but that doesn't make it any less fanfiction.
Fiction is specifically not based in evidence.
A theory is backed by evidence.
When you ignore the presented evidence for a theory, and call it fanfiction, it makes you sound like a flat earthier. The type of person who looks out across their back yard, and exclaims the science is bogus because they can't see a curve with their own eyes. I know you can be better than that.