I am an only child. My parents, like every parent out there (the good ones a least) did the best they could.
I am rarely ever lonely. I was given a fabulous gift of being able to make friends easily. What's that myth about being socially awkward? BS! My parents are military and we moved every three years. I'm sure some of you pseudo-psychologists would just gasp at the horrors of making an only child move every three years. "The horrors!" But guess what, it's taught me a very amazing lesson. Flexibility. Now I have friends who live all over the world. Where I live currently, I have a tight and fabulous group of friends that I consider family. When my home was broken into two years ago, these friends all came out in support offering to help my husband and I clean up our home to offering us a safe place to live until we could move to giving us money *lol*. Yet, I have several friends who can't even speak to their brothers or sisters due to stupid sibling rivalries from childhood that never got resolved.
Granted - I miss my mom and dad. We get to see each other once or twice a year. But I have learned that if you're heart is open, "family" is waiting for you wherever you go.
Yes, there was stress growing up - I'm sure it was the same for any first child. Parents, good ones anyway, worry about their ability as parents. The first and only child is often the guinea pig for their parenting skills (what works and what doesn't). But again, I'd not change one dang thing my parents did. I love them. My dad is my hero. My mom is my heroine. They taught me character. They taught me laughter. They taught me how to be an individual and independence.
I work with college aged students now. I see what "over-parenting" looks like. And it has absolutely nothing to do with whether or not the child is an only or has siblings.
You want to group and generalized. Go generalize yourself.