Discord is written exactly like Q, a character from Star Trek Next Generation: an omnipotent god who thinks it can play as he wants and he is above petty concerns like house, gravity and stuff. Slowly he learns these petty concerns are the very life of others and he should respect that.
and no, never it was shown "soulless". In MLP:FiM, he jokes with Twilight, speak to her, in a way he understands her and he is delighted when he is sure to have won. He has a twisted humor and goal : to be free and spread chaos.
But he is not a monster: he doesn't kill ponies, he is not violent. In a way, it's a character drifting apart, without connection to people he's craving for. Like it happens in Q in star trek (where the Q character looks after acceptation by Captain Picard and in a way to help him to understand future of humanity), the Discord character is obviously fit for a story about friendship.
Discord is a trickster in a child show. He can be evil, and for the most part, he will be good, but he stays a powerful rogue power only keep in check by the magics of "friendship" who is the whole point of the show.
truly, never he was shown as a "soulless monster" in MLP:FiM, and the fandom seems to have seen it for what it is: a over-the-top trickster. There are many fan pics, stories or tumblr where Discord can be pretty dark but can be reasoned and in fact he is driven by interactions with others.
There are also fandom ideas where Discord drifted in extremes after some broken relationship with Celestia, or he was responsible by mistake (a joke going horribly to far) for the whole Chrysalis becoming a changeling (and then he went in endless jokes about futility of the world) and so on.
he is NOT like Q. Q had well intentioned motives from the very start. and Discord did horrible things, he mentally raped the main six just for fun. and even if he didn't kill anypony, he still didn't care about the mortal danger he put all the ponies of Equestra into. and in a kids show, villains can't be complex, using TV Tropes words, in a kids show, a villain is either an Anti-Villain or a Complete Monster.
Q intend to kill all humanity just if a star fleet team fails a mission. well... and Q killed someone !
and after, he appears in the enterprise to satisfy his fancy with new games or challenges, or personal problems. In time, he mellows a little, becoming a somewhat troublesome friend. Like Discord. It's the very same character, like intended by the authors. Even the actor plays it the SAME.
- He doesn't care ? but he doesn't put them in mortal danger. he makes a mockery of their world. In a way, Pinkie Pie could have liked a world with chocolate rain...
"bad writing" (and no, he disobeys the Q quantinuum and was restless as Discord, and it was the point of a whole star trek episode)
I understand you don't like theses characters, but my point is not about consistent writing, but just one simple point : "no, the character was not 'pure evil' in their first appearance, so yes, the writers have some flexibility with them".
If tomorrow, Sombra come back and become the best friend in Ponyville after singing with Sweetie Belle, okay... it would be too much
- Heck, Even Chrysalis has still enough personality and depth in her to be able to write a stories where the ponies have to work reluctantly with her for a common good. (and beside Chrysalis is evilly working in the interest of her own evil people )
- "Discord is a monster, he even clearly committed genocide in the past."
we already have seen nothing in the show support that. You will not convince anyone by repeating it. The show is available on youtube to see. nowhere is "murder". there is no genocide in MY little PONY. It's not a grimdark fanfic. "Cupcake" is not canon.