A good question indeed. My favourite game from the series is Dark Souls 1 and it is the one I am playing the most often, so expect a biased answer and a small rant.
After the success of Dark Souls 1 FromSoftware really went ham with the whole "hard game, you are going to die"-shtick (some examples being the total death counter in Dark Souls 2 and naming the Dark Souls 1 pc port "Prepare to Die Edition"). They also began to ramp up the 'difficulty' by changing various aspects of their games, like the general speed of their games. Beginning with Bloodborne (PS exclusivity be damned) their Souls games began to get quicker, enemy animation more annoying (and unrealistic in some places) and demand for quick reactions higher.
Of course, you can argue that part of the problem is also the fans who get better and better, demanding harder and harder content, which creates a vicious circle (I heard that in the Elden Ring Shadow of the Erdtree DLC this got even so bad that they had to nerf a boss or he would have been hardly beatable or something). However even then there should be a point where you say stop, nada, this road just leads to a dead end.
Problem is, FromSoftware has made a good name with these titles and the general feeling their games have, so of course they will continue this path, milk the cow until it's dead. Don't get me wrong, I like Dark Souls, but I have gotten so exhausted with their newer titles that I don't even bother anymore with those. Sure they might have the newest shiniest graphics and more multiplayer activities but who cares. Their presentation of game lore also gets really tiring in the long run, but this would deserve a post of it's own.
Now, of course Dark Souls 1 isn't perfect, far from it. The second half of the game is really weak compared to the first half and the overall game design could use some serious reworking (the control dump in the tutorial is horrid for newer players) if we think about it. But at the end of the day, I prefer it's slow, methodical combat over the fast, erratic button mashing of the newer titles.
To perhaps get back to the original question, yeah, the series may have adopted some bad game design from it's ancestors (Demon Souls, Dark Souls 1), but the true problem lies in what the developers (or the higher ups who get the money at least) want you to think of their games. If you make something with the intend to be just hard, requiring multiple (in times even unnecessary) runs to finally beat a boss, then you will get this as a result. If it is supposed to be challenging then make me really feel that it was my mistake that led to my demise, my overconfidence, not a weirdly delayed attack animation that instantly killed me.
...or perhaps I am just getting too old in my youth

.
Thanks for coming to my TED talk.
Never change Sseth. Sadly a probable outcome for anyone new trying the game. To add something, the massive open world may be fascinating and wonderful the first time you play it, but it gets annoying when you replay the game and have to zip from one place to another to check your checkboxes. Some Youtubers that I watch (better than playing

) have expressed this annoyance a lot of times already.