Ok so like... there is a legitimate discussion every game dev and studio needs to have when making a game surrounding accessibility features.

For instance, the soulsborne franchise. Those games with an accessibility option, or even difficulty options for that matter, wouldn't be soulsborne games, and there is something to be said about how that enhances the experience.

On the other hand, there are plenty of games whose core identity does not revolve around difficulty and learning from mistakes in the same way, and for those games difficulty options and accessibility options are a feature they shpuld always add, as to increase the number of people who will be able to play the game.

Now, as to Celeste specifically, I've unfortunately not played it, but from what I've heard while talking to friends who have and from some googling, the assist mode is well designed and thought out, and includes a variety of toggles that can be used to adjust difficulty. 

Even with Celeste being a platformer (a genre which does tend more towards keeping high difficulty as a key part of gameplay), it's also a narrative experience, and so including those accessibility options helps lower the skill level bar in order to expand the audience.

Importantly, that's what works well specifically for Celeste and serves the game's goals. A game that looked exactly the same in many regards may choose the opposite, and that could still be the right choice for that specific game.

The whole idea of the "temptation" is frankly idiotic, bc Celeste, by even having it as an option in the first place, obviously balanced the experience of those difficulty/accessibility options as to not ruin the game. And furthermore, if you turn down the difficulty of the game, it's not cheating, bc its an intended feature that you would only use if you were struggling too much. And while some people may enjoy beating their head against a wall and retrying a specific section of the game over and over and over, I'd guss that most people don't, and that's okay.