Xebec had higher portrayal until GV, but I think Roger and Whitebeard ended up with higher portrayal because
> Roger ended up as pirate King and Whitebeard known as his equal
> It was mentioned that there has never been any bounty in pirating history higher than Roger and Whitebeard's
> In Kaido's mind talking about the people capable to fight/beat him, Oda drew Roger and Whitebeard on top
Even in his best portrayal, Xebec is mentioned as "perhaps" Roger's greatest foe, and it could be because they both had the ambition to be pirate king/King of the world when Whitebeard was never interested
With that said, depending on his age, it's not impossible that he didn't reach his peak before dying in GV since it was mentioned others like Whitebeard and Co grew stronger, so not impossible that his peak may have ended up higher if he didn't die at GV
But Blackbeard will probably show that potential or higher when he reaches his peak zehaha