The problem until a little time ago, or even now, was that Luffy beat the supposed strongest creature. Now Oda is probably upping up the roof again introducing these 9 knights, showing Shanks power and evebtually making BB grow in power again (he will probably get his 3rd df soon, before he awakens the yami eos or little before it). So they are probably new characters, at worse they could be "zombie" versions of deceased legends (Xebec, WB, Roger) but that will be a big blow to what is left of the quality of this manga. So we have to wait.