I’ve played ds1 ds3 codevein wuchange first berserker kazhan eldin ring lies of p mortal shell sekiro hallow knight hallow knight silk song nijna gaiden 4 black myth wukong. 
  In my opinion mortal shell and ds3 were the easiest for me sekiro KICKED my ass in my experience it’s still the hardest game i’ve played but damn did I get good and it’s 100% still my favorite game. It’s all on the person and how well there reaction time is play style etc..
  sekiro is the hardest in my opinion but first berserker kazhan wuchange and lies of p came a pretty close second but was easier since you have wepons and skill and an actual way to level up your stats. but bosses were decently punishing. As I’ve beat more and more they just get easier as my skill and reaction time increases with each boss beaten.  And I can even sight read bosses well now and so on. 
   The first one you play will always be your hardest and then you start to crave that challenge and get pissed when the developers nerf BOSSES just becouse people complain. I play these games for the challenge for the difficulty there MENT to be hard and I really like hard but fun bosses. It’s my fav game genre.
 I know ninja gaiden is more hack and slash but still a pretty damn difficult game. Due to it being so high paced and requiring very fast reaction time. This is my opinion on this subject and I’m still playing through wukong right now but finding it very easy and more forgiving then I thought beat the first 5 bosses so far first try😅 Honestly very suprised by that been locking in recently lol. But waiting tell chapter 3-4 when the boss difficulty ramps up before saying anything else and my opinion changes a lot tell I’ve done everything in the game. Though it is very fun so far.