they don't have any form of advhaki which they will and they are already beating someone Roger couldn't, and from what we have seen a haki bloom is a multiple factor of strength.
And he received multiple haki blooms to make it happen
But he will eventually eat him, why wouldn't it be the same for Roger and Mihawk?
Mihawk and Shanks had their fights way later but from portrayals we can safely assume that they have both surpassed Roger but are still inferior to Ryuma
We don't know anything about Mihawk, for all we know he might be Imu, or he might be the thing that will stand in Luffy's way of achieving his goal, a goal Roger failed at
Chinjao had misinformation, we already know that Roger didn't surpass the yonko(Whitebeard and Big Mom) or admirals(Sengoku or Garp) so when Luffy beats Kaido and surpasses him it already puts him over what Roger ever did