Time to accept 3 facts.
(1) Saint Shanks is a Swordsman.
(2) Roger is a Swordsman & Saint Shanks/Roger both use the same style of combat like Yamato/Kaidou.
(3) Mihawk's Swordsmanship > Roger & Saint Shanks.
Mihawk was just not the Strongest Swordsman in Roger's Era, he is in Saint Shanks' era.
Mihawk & Saint Shanks being very close to Roger is a possibility now.