To answer the OP's questions.
Yes, difficulty modes are accessibility, a brute force version but, easier to implement I expect than what would be my gold standard (Sliders to customise difficulty to each individual, and options to turn HUD stuff on and off like mini maps, markers, visual guides etc.) What is 'hard but fair' to an able bodied person may be insurmountable to someone with a physical disability or a processing disability, so, even if the 'dev's artistic vision' is a hard but fair game, they're not providing it by not providing options in both directions.
Yes, I would say it's ableist if you (i'm using a general you here, not specifically calling OP out), an able bodied and/or neurotypical person, does not want accessibility options because 'reasons'. And, to quote myself from the other thread, an artistic decision that's inherently ableist is still...well, ableist. And we should be moving away from that. Options are simply that, options. Each individual can choose the experience that is optimal for their enjoyment, and the options that are best for them.
And to be frank, we already spend a lot of our time with creators who don't implement accessibility or difficulty options, or implement them in a mocking or derogatory way, as well as pressure from the wider gaming community to simply 'get gud' or to be completely dismissed in any conversation around the game if any accessibility concessions are used. 'Accepting it' is what has already been happening, just to stay in the hobby, or to keep the peace because whenever people ask for accessibility, if people aren't in the 'acceptable' range of disabilities to provide concessions for (visually impaired or hearing impaired, primarily), people get angry, or people call you a baby, or tell you to leave the space.