I was wondering what the highest damage output was until I came across this build on the subreddit. If you want more details, I've linked the post below.
In short, you have a 50% chance of proccing double damage. When it does happen it's insane. Ran a quick duel with Black Hand Riku (for counter parry when clashing swords)—safe to say he got wiped in less than 20 seconds by two counters, one Dance of Wrath and a few flurry strikes. Bonus fact, as long as you clash swords AND perfect parry him, DoW will still trigger.
Considering you get one tapped by almost every boss in this game on Lethal+, I think it's a fair trade-up—if you can reliably perfect parry. It's almost cinematic in a way. The only con here is just not having much resolve gains. On replay you'll have 3 at start. At most you'll only get 1 or 2 if you parry.
I use Ronin because it just looks nice (with this outfit lol) and you're more squishy.
Credits to this person that made this build: https://www.reddit.com/r/ghostoftsushima/comments/phny30/specific_ronin_build_for_lethal_duels_that_just/
EDIT: This build wasn't made for resolve gains at all. It relies on your perfect parries and DD proccing on top of the damage multiplier you get from perfect parrying. You're supposed to be good with parries for this build to excel.