Vivace 
“ShimSham my GlimGlams”
Tbh, I don’t think there’s a way to make it more sympathetic, particularly while keeping all else the same. I think that eliciting sympathy was NOT the real goal of revealing the backstory. It shows how Starlight came to see cutie marks in a negative light; it highlights how sophomoric her philosophy was by having the experience occur while she was a child, before she had matured emotionally and mentally; and it nicely juxtaposes how she was metaphorically stuck in the past as she had literally been every time Twilight entered a new timeline until she was physically brought into lifeless Equestria. _*Cutie Re-Mark_* spent all the episode showing that Starlight had crossed the moral event horizon, assuming that her methods of induction into the philosophy of her Village of Equality weren’t convincing enough, so to try eliciting sympathy right after leaving the wasteland is pretty silly. As long as she acted with agency, nothing that had happened to her could make Starlight’s evil justified; shitty experiences don’t excuse being a shitty person.
Because of this, a backstory that looked like a raspy plea for sympathy at face value alone seems more like a front in retrospect, like the artifice is deceiving you, just it was designed to do. Detailing more of the steps between the catalyst and her debut really wouldn’t justify her anymore than what was shown, but it would give more to objectively point to and understand; not that speculation should be spurned since imagination is a wonderful tool, which we’ve used for other ex-villains. I’ve honestly never been bothered by Starlight’s backstory, and certainly never moved to anger over it, and the fact that even Twilight calls Starlight’s takeaways from the experience ridiculous, and even told her what she should have done in response to her catalyst- to try again instead of isolating herself- tells me that the writers weren’t utterly unaware of what they were doing.
Starlight’s backstory is about escalation due to poor coping, and a lot of people have coped badly with stressors in their lives. We’ve all been immature and overreactive at some point in our lives. Not as many can say that they let things escalate to the degree Starlight did, no, but the solution to halt or prevent escalation is simple, at least to say: let go of the past, and keep moving forward. It can be developmentally stunting not to.
Because of this, a backstory that looked like a raspy plea for sympathy at face value alone seems more like a front in retrospect, like the artifice is deceiving you, just it was designed to do. Detailing more of the steps between the catalyst and her debut really wouldn’t justify her anymore than what was shown, but it would give more to objectively point to and understand; not that speculation should be spurned since imagination is a wonderful tool, which we’ve used for other ex-villains. I’ve honestly never been bothered by Starlight’s backstory, and certainly never moved to anger over it, and the fact that even Twilight calls Starlight’s takeaways from the experience ridiculous, and even told her what she should have done in response to her catalyst- to try again instead of isolating herself- tells me that the writers weren’t utterly unaware of what they were doing.
Starlight’s backstory is about escalation due to poor coping, and a lot of people have coped badly with stressors in their lives. We’ve all been immature and overreactive at some point