User blog comment:ChiroSamai94/Brook the last crew member?/@comment-3060121-20120501153225/@comment-4493594-20120502162849

I could write an essay about why you missed the point but I'll keep it brief:

"Filler members" would be expendable. If there is one thing we learned during OP it's that no crew member is expendable and that the entire crew would go through hell and engage the devil himself just to save one of their crew men. Now if Oda introduced filler members everything until now would become banal and insignificant. It would just kill the whole heroic spirit.