@nik87 Whitebeard was highlighted above the other Yonko on several occasions. Being called king of the seas, being hardest to take down according to Big Mom, being the equal of "even" Roger according to the narrator.
Oden saying that no one can beat him if he himself can't, obviously referred to the people within Wano, which is a closed country. Otherwise, that statement would also put Oden above Primebeard. "If I (Oden) can't beat him, then Whitebeard as well can't". Isn't really logical. Roger swatted Oden away like a fly.