I'm talking practical. I know you can reduce networks further BUT there is plenty of stuff that could break.
So from the point of abuse logic it's appropriate to treat the whole /64 as a single unit. (That was the starting point of the thread, even though I realize that due to thread drift that's probably not what your comment was about.)
This RFC has things that may not work properly not to use /64. https://datatracker.ietf.org/doc/html/rfc7421#section-4.2