I guess I don't understand why birth order should matter ultimately? I don't think that in and of itself is a reason to feel sorry for someone. Every family dynamic is different. In my family, I feel sorry for the youngest because she was kept a perpetual child and not taught to be independent early enough and she's struggled her whole life.
In my husband's family, he's the baby and the one that turned out the best of the three. The middle girl is a chronic drama queen who manufactures stories for attention all because she's jealous. She can't have kids and the other two did. I used to feel sorry for her, but she is ridiculous and mean spirited so my sympathy waned greatly. I guess she's your stereotypical "attention starved" middle child. My hubby though is the most responsible and proactive of the three despite his mother babying him so much. He pushed back for his independence.
My sister in law, the oldest in the family above has 8 children and won't stop popping them out despite being in poverty. She was the oldest so should have had more responsibility and knew better right? wrong. She's irresponsible and her brood now suffers for it. She's addicted to having babies or something. All the kids raise each other. I feel sorry for all of them first, last and everyone between.