I kept going back and forth on this topic when I first woke up and honestly? I disagree with the OP and I also have some issues about how difficulty encourages you to "get better", specifically due to people plateauing and having disabilities.
Let me explain a bit from my thoughts about what difficulty is and isn't.
Difficulty is a subjected level of how "difficult" a game will be to an individual playing. Many times, people look at difficulty in a binary sense, where it's "easy" "normal", and "hard', but the reality is that the individuality of each person who plays a game, will have a different experience on each difficulty. Before I get into the disability angle of this, the fact of the matter is everyone is going to have a plateau and limit to how far they can get in a game. I actually think the Souls/Soulsborne/souls-like are absolutely horrible and terrible for this, because players will go into these games and reach their plateau and never be able to overcome it because of this.
Many players have a limit to where their skill level can take them on a game, in which the games only having a default "difficulty", can gatekeep even these players. Difficulty in itself can never be really categorized in the same sense of binary conditions, because at the end of the day, people will have different skill levels and different needs to succeed. There is no actual "good" and "bad" difficulty, because you can't define something that is not even binary.
But what if the difficulty is at odds with your disability and a mode that many people would find objectively "bad" because the difficulty is too easy, is significantly difficulty for players who have said disabilities?
I'll speak on my experience as a disabled adult.
Disabilities, unfortunately, affect my ability to play games. They range from "slower response time", "depth/visual perception and unable to understand spatial relation", and I also have an issue where my brain has a limit of how many processes I can have using my fingers, in which prevents me able to do games with numerous button combinations: It will literally cause my brain either to become confused and extreme cases, cause my brain to freeze up/misfire resulting it weird reactions to my movement of my hand and body (this happened with me on the chopping minigame for Ratatouille minigame in Kingdom Hearts 3). I also have other issues but I'll focus on this for now.
One thing that I run into and it's a problem a lot is the button/hand limitation I mentioned and slower reaction time. When I was playing Stranger of Paradise: Final Fantasy Origin, I had to drop down to Story mode, because of the problems I experienced above. Story mode was "just" enough to help me with my disabilities in which I couldn't overcome limitations of my own disabilities and I'll be frank: Story mode was exceptionally difficult for me at times and some of the later areas and bosses really pushed me over the edge at times, notably the final boss. If I'd been forced to have even used Normal mode, I don't think I'd been able to have the best experience.
But I've seen people fine "Story mode" too easy, but for me with living with disabilities that limit my button usage and reaction times, it was enough to be able power through some sections and still find it enjoyable, but difficult experience.
Difficulty is extremely subjective. What makes a good difficulty for one person, another person will find bad. Especially once get into the fact many, many, MANY, gamers have disabilities and even these difficulty options can assist with making the games both more approachable and accessible to said gamers. There'll never be an agreement on this subject, because it's individualistic in nature and it's subject to each person, both down to plateauing on skill level and disabilities.
The only thing we should agree upon is really pushing for making games more approachable and accessible for gamers. Not what makes a "good easiness" and "good difficult game", because it's core, it'll be subjective.