Consider: Starlight, born an Earth Pony, but she committed some crimes against magic and science to graft a magical artifact onto her forehead to act as a horn.
It's very rare for Earth Ponies to have Talents in complex magic, so when it does happen, it can either be a source of great inspiration and creativity, or a disruption and "challenge" to the "natural order". In the case of Sire's Hollow, there was a major economic divide between the wealthy Unicorn children like Sunburst who were all pushed to go to Celestia's school if they showed enough magical ability, VS the Earth Ponies who made up the working and servant classes and sent their kids to the local public school. Sunburst's Cutie Mark was what set his path in stone; up until that point, he'd struggled as a student, and was one of the few Unicorns to go out of his way to befriend an Earth Pony. But of course, she couldn't go with him.
This is what started Starlight questioning the structure of their town, the power of Unicorns over the other "races", and how much work went into maintaining those pipelines. Her distrust for Cutie Marks comes from the fact that while Sunburst was "loved" but actually got torn away from everything he loved for his talent, people just saw her as confused about her role in society - a waste of a talent.
So, if everyone was so sure an Earth Pony couldn't be as strong as a Unicorn, she'd just have to prove them wrong, by bridging the gap with her "wasted" talent. Y'know the staff she used for the Cutie Mark spell? She started growing that tree as a small child, and carved a horn for herself out of its wood, along with the staff, which she could use to weave more complex spells. This means that, since the horn isn't part of her body and can't feel pain, she is not held back by the limitations of migraines, inflammation, general brain fog and the like that usually comes about as a side-effect of overusing magic.
However! This also means she's not very good at telling when the rest of her body is overloaded, and will brute-force her way through spells that would've concussed a natural Unicorn several times over, only noticing the damage it's done well after the shock wears off and she's ready to pass out. Over time, the fibers of the horn grow into her skin, connecting more closely with the rest of her skull; she refuses to acknowledge that it's starting to hurt, not just when she's using it, but *constantly,* because her body is struggling to adapt. It was supposed to make her stronger, she can't give up now! After everything, she can't stop until she's proven her point - proven she's worth more than they ever expected, that she's better than them, that she knows what she's doing and they were wrong for letting her slip through the cracks like that.
So what if it's destroying her in the process? They didn't care then, why should she care now? She's stronger now! She's not a weak little fully who can't defend herself, she's Starlight fucking Glimmer and no man nor mark will tell her what she can and cannot be! Hell, she was actually doing a bit better when she first lost faith in Cutie Marks, because for a moment there, she started to genuinely believe she was worth something beyond her talent...
She's not just "what would've happened to Twilight without friends". She's "what would've happened to Twilight if she were born in a slightly different circumstance, which made people see her talent and intelligence as a threat instead of nurturing it to be exploited later".
Earth pony Starlight Glimmer has SO MUCH POTENTIAL as you’ve shown written here! I love the idea of Starlight tapping into magic that her body isn’t used to or made for and it’s consequences
Every pony species has magic. It’s all about how it’s channeled through the body and their base magical alignment. Starlight Glimmer would be a rare example of a pure magic alignment for an earth pony. And all she’s heard in her life is how much untapped potential she has and how it’s being “wasted”
The staff and her “horn” being created from the same material is a brilliant idea! And the horn digging into her skull is a fascinating idea.









