It is because a sword can't cut him so Roger loses
phoenixashura
for everyone who says roger can beat whitebeard notice how while whitebeard was fighting roger he was only using his sword and the fight was balanced so just imagine if he used his fruit during the fight
Muxmimi
In my opinion, Luffy will not lose against Roger because Roger himself once said that someone would be able to surpass us and what he meant was Luffy's own group and don't forget that Luffy is the main character in this film.
venesabisnis
Roger physically cannot live at the same time as joyboy
