i put senti above duelist because the majority of fights you take as a sentinel are in your favor, whether it be off a lurk timing or your util forcing the other player into a bad spot.
a duelist can at best take a 50/50 fight. if you play jett/raze the only consistent way to get an advantage relies on your teammates properly supporting you and in ranked that isnt a reliable strategy. the others have flashes/stuns that are shootable, turnable, or avoidable with good positioning.
not saying duelist is hard and the difficulty gap between senti and duelist is very small imo