@Evil Emperor Proteus

@Proper Prose

Actually, “The Devil” Arcana makes sense for Sunset - just from the Megami Tensei wiki:
“the negative aspect of the Devil Arcana represents the urge to do selfish, impulsive, violent things, and being a slave to ones’ own impulse and feelings. Occasionally, it is also portrayed as a symbol of temptation. The positive aspect, however, represents a healthy bond or commitment.”

http://megamitensei.wikia.com/wiki/Devil_Arcana

Or other descriptions of what the Devil arcana embodies: represents: Being seduced by the material world and physical pleasures; lust for and an obsession with money and power. Also: Living in fear, domination and bondage; being caged by an overabundance of luxury; discretion should be used in personal and business matters.

It’s upright meaning is: Shadow self, attachment, addiction, restriction, sexuality

It’s reversed meaning: Releasing limiting beliefs, exploring dark thoughts, detachment

Doesn’t this fit Sunset quite well?

A lot points out Sunset got worse in th human world (was seduced by the material world); Had originally lust for and an obsession with power; Living in fear, domination and bondage - “damnation and bondage” can reffer to Sunset’s state before and during the first movie (ie she stated she didn’t know nothing of friendship), she lived in fear in the Rainbow Rocks, caused by her guilt, before managing to overcome it. (Also in part in Friendship Games)

Shadow Self - Sunset Satan; attachment - Sunset’s old obsession with becoming an alicorn, getting the Element of Magic, and latter attachment to her past guilt.

Releasing limiting beliefs - Sunset welcoming friendship, and changing her ways; detachment - how Sunset overcame her old obsessions, and managed to develop beyond the past that caged her (as even the My Past is Not Today animation shown.)

https://en.wikipedia.org/wiki/The_Devil_(Tarot_card)
https://www.biddytarot.com/tarot-card-meanings/major-arcana/devil/

Even other descriptions of Devil, connect the arcana with obsession, and alternate descriptions, have similarities with Sunset:
https://www.thetarotguide.com/the-devil

upright meaning:
Addiction, depression, mental health issues, secrecy, obsession, cheating, dependency, bondage, materialism, sexuality, powerlessness, hopelessness, abuse, violence, assault

depression - Sunset in part in Rainbow Rocks; secrecy - Sunset originally hid her true intentions to anipulate people, including Vice Principal Luna in the first movie; obsession - as i stated above; dependency - this one is a bit more complicated - as after redeemption, Sunset was fairly dependant on pony Twilight - in Friendship Games doubting she could hadle things without her; powerlessness, hopelessness - again, Sunset’s issue in Rainbow Rocks; abuse, violence, assault - Sunset before she was redeemed was a bully, and while she didn’t use direct violence, she did assualt people verpbally and intimidate them, as seen with Fluttershy.

Reverse meaning:
Detachment, independence, overcoming addiction, freedom, revelation, reclaiming power, reasserting control

Detachment - as stated before; independence - how Sunset, while still respecting pony Twilight, overcame her dependancy on her in Friendship Games, in part to save another Twilight (Sci-Twi); revelation - Sunset’s redeemption, and various parts of her character development; reclaiming power , reasserting control - Sunset overcoming her obsessions, as well as being latter weighted to much by the guilt of her actions.

Again, “doing selfish, impulsive, violent things, and being a slave to ones’ own impulse and feelings” fits SSunset during and before the first movie; and “healthy bond or commitment”, represenets Sunset’s commitment and bond with her friends, especially both Twilights.

Another thing, although kinda connecting to the cool factor, is that Sunset kinda fits to a Luciferian character archetype (even far beyond just turning into a demon), hence people connect her to the Devil Arcana - although Satan/Lucifer (note: not in SMT terms, although SMTIV: Apocayplse kinda muddied the grounds) himself could be as well connected to other Arcana, like the Fool, or Hanged Man.

I mean, Sunset’s falling out with Celestia has some similarities of Lucifer’s rebellion, and Sunset even exemplified the two sins connected to Satan and Lucifer - Wrath (Satan), and Pride (Lucifer) - and she still shows a bit of anger issues XD