I have no facts and no arguments either, but it is only an impression since they resemble their personality a little, that are free, and that no one hurts their mate, and they are both left-handed. Shanks may have been inspired by Roger and his fighting style; they even seem to use the same sword.
I also don't think they are just ordinary swordsmen, they didn't even bother to make the sword permanently black, even having CoA top tier. They must have other powers that channel their power, my guess would be both having the unique power of channeling CoC as a form of atomic energy that would work similar to Fujitora's ability; Oda when talking about Shanks on SBS put the question: '' How does Shanks really fight?''
Probably Shanks has the strongest CoC shown so far, so I don't find it impossible for him to have a unique power that only Roger was able to use. And Shanks managed to arouse him when he lost his arm, causing him to gain a PU for he be stronger and become a yonkou in the following years.