I think the crux of the issue here is that Sekiro demands you play (down to almost a per-encounter manner) in a very specific way, more than Souls or even BB asked of players. That way of play is not for everyone and seems to be for less players than any previous FROM game has been, based on the ongoing debate. Unlike previous games, there's also no way to make the encounters easier by "grinding" for levels so you can buffer your mistakes or brute-force things - you either figure out each puzzle as laid out, or you don't progress. Early skills aren't great boons to help here either. This puts the grind completely on "training" and mastering the combat exactly as they want you to play it; it's more fighting game and less action game at this point.
Also, fighting mostly humanoids of my player's size makes the read area of the screen (the pixel area that gives me information that I need to respond to) a lot smaller than any previous FROM game, where monsters had more unique and grander tells far beyond the subtle stuff we see with human opponents here. I think this is why the General on the horse is the best / most fun fight early in the game - it's big and readable. It's also why I bet the special attack indicator (grabs, etc.) was added as an attempt to make things easier on players.
Personally, I like Souls / BB better because I have room to play differently than my friends, and that makes for interesting conversation; Sekiro isn't a game I'll ever NG+ because the experience is so focused on only one way to play, and it's not my personal favorite.
Really, if they wanted easier difficulty, all they'd need to do is increase the times on attack windups, so you have more frames to react and know what the correct rock/paper/scissors counter is to the moves that are coming at you. You'd still have to learn the combat and tells and not get hit, but at least you could react better to what was coming your way for a limited time window. A slow time prosthetic that just lets you see a read here and there would do it. IMO, of course.