"Would The Father of All Alicorns do something similar to that? Use something that happens between Draconnequs to teach an Alicorn a lesson about their concept?"
Possibly. But he'd treat it less like a dinner and a show like Havoc did (which is WHAT pissed off Amicitia about it, and Havoc was DELIGHTED she had the guts to call him out on it). And make doubly sure his child was safe for the whole thing, and likely wouldn't have made it a front row seat just so not to demean those present. Also, Rancor is violence, so it would be wrong NOT to expose her to it to help her properly development. This isn't true of others.
"If a Draconnequs had gone to Fauna Luster and asked for something the way that Celestia asked for something from Entropy (which then she messed up and it turned into the Windigoes), how would Fauna Luster had reacted?"
She'd have been less BRUTAL about it. And given she is EMPATHY INCARNATE, she'd likely consider the draconequus' point of view a lot more, and give the instructions in their language, on their level to AVOID such mess ups. Entropy's supreme apathy made that nearly impossible for her: Entropy due to her nature didn't care if Celestia messed up or not. Fauna Luster, being empathy WOULD HAVE CARED about the out come.
"Entropy helps Applejack in the grounds that if she becomes Veritas then she would help save Chance by reforming her. Would that be a correct motivation for her?"
That normally goes against the grain, since apathy is a BIG PART of her personality. Those who win or fail mean nothing to her.
Though there is a reveal soon that would change all that. But it would be a spoiler to tell you. But it would fit PERFECTLY with what you want here. Do you want that spoiler so you know how to fit into your story perfectly? She is the embodiment of heat death, the end of all things.
A friend suggested this:
"It'd probably be the aspect of her representing the end of evil or the end of sin or the like.Or the end in the sense of the death of the old person and the rebirth of a new one."
Again, a have a perfect reveal that would be PERFECT for this, but it's a spoiler. Do you want me to tell you it via private message?