Katanas are meant for hit and run strategies. If you are to fear anything in this game it is a person who knows this and can perform an instantaneous running rb with the katana.
I've had no problems with katana users because most of them just spam, or have really telegraphed/predictable patterns when they go for a rolling or running attack. Like I said before the person to fear is the one who makes his attacks instantaneous and un-dodge-able; this can be said with any weapon. However, these people are few and far between.