If a game doesn't have difficulty settings, then I think it should be on the easier side for proper accessibility.
If a game has difficulty settings, devs can go wild as far as I'm concerned, but I'm definitely in the camp where I'm starting to feel like story-driven games could almost become walking simulators on the easiest setting just so everyone can experience it no matter their ability.
However, the best games have difficulty settings that are carefully tailored. I mostly play JRPGs so for those, most of the time when they have a difficulty setting, what they really have are stat multipliers. So, for example, on normal mode everything is 1x, but on easy, you might do 2x damage and receive 0.5x damage, and so on. But great games? When you up the difficulty in those, in addition to basic multipliers that make the game harder, they might change the attack patterns of enemies and bosses, meaning you have to play strategically instead of just brute forcing your way through everything and it's always so much more rewarding.
As for learning curve, I guess I prefer when elements are introduced gradually. If I get too many tools at my disposal from the very start, I'll often end up just finding whatever basic thing works really well for me at the start and stubbornly use it all the way through because I'm bad at video games, apparently. But if I get new skills/abilities/weapons throughout the whole game, I'll be much more inclined to experiment and try everything, which I think leads to a better experience all around, even if I end up going back to my tried-and-true original strategy anyway ahaha.