Living under the shadow of a perfect big sibling can really be hell, especially when you're younger.
I never had that problem, even though I'm the youngest, but it isn't uncommon to see people whose family relationships were seriously damaged because of it.
One thing that stands out is the attitude of the MC's parents; they actually seem pretty supportive. One of the most damaging parts of this kind of situation is when the parents are the ones constantly making the comparison and being toxic about it. That feeling of "My parents gave up on me for my perfect siblings" is a disaster for any teenager.