Vista didn't how anything superior to Mihawk on Marineford. Other than the clash, Mihawk has some great showings in there while Vista has nothing else.
Mihawk does whatever he feels like doing, that has been true to his character since his earliest introduction.
What Oda said about Shanks was simply that we hadn't seen Shanks fight yet. And even within swordsmanship there are plenty different styles. Shanks has always been a swordsman.
WRONG
Vista has got a better showing than Mihawk
(1) Akainu was about to kill Luffy , standing over Luffy
(2) Vista with the help of Marco helped push back Akainu
meaning Vista helped disarm a very perilous situation
That is to me a much better showing then cutting some ice with a slash that was stopped by Jozu, virtually an equal to Vista