Oh yeah I 100% agree with you! I always try to make sure to point out all the other options available to people if they’re frustrated with difficulty. I think people don’t understand that a lot of the ‘options’ in Fromsoft games are not in menus - they’re baked into the gameplay itself with in-world/lore reasons for doing them. Like how co-op uses a sign instead of a multiplayer interface ‘room’ like most other games.
It is the best thing about Fromsoft games IMO, that everything is a vessel to help tell the story and create more immersion, and a difficulty slider is game-y and creates less immersion (as well as what you said - would ruin the opportunities the difficulty affords in directing pleayers).
All that being said, if they added a slider that would only affect others, the only way it affects me is that I’d be bummed that they didn’t get the great experience that I love about the game. I mean the other person mentioned Celeste which I also really enjoyed and I wasn’t even aware that it had difficulty sliders. So that’s how much they’d affect my enjoyment of the game.