I will say however, there is legitimately a decent chance “haki wizardry” is real and Roger(and probably Shanks) do have some power beyond mere swordsmanship.
I only say this because both Whitebeard and now Xebec seem to have had legendary busted DFs on top of their already top tier advanced haki and combat skills.
If Roger was even comparable to WB, then he must have had something to rival the gura. And coating his blade in haki wasn’t it, because WB could do that too.
It is very odd how a storm supposedly destroyed Shiki’s crew while saving Roger.
That said. This is all speculation and from everything we have seen thus far, Mihawk has better swordsmanship than Shanks and probably Roger too.