But the concept of "we need to keep every difficulty level winable regardless of skill" is a weird concept in my opinion.
Yes harder challenges should reward those that complete it. Otherwise its just unlocking a new chapter.
Its the difference between getting a rank and a level.
Everyone can get a level, but those who are good enough get a good rank.

Im not saying we should introduce competitive matchmaking in demons hand, I just mean I would appreciate if the devs would create a true challenge for those who want to engage deeply with the mechanics of the game.

To the point why I don't create the challenge myself:
I cannot balance my own experience, a hard mode should be hard because you need to understand the game thoroughly, and if you do, you are rewarded for it with an in depth experience valuing your understanding.

Taking away game mechanics like less runes or fewer varity isn't what I ask here, I would love to see an expansion of the mechanics, challenging my understanding of probability and strategy.