I never understand these threads as all they ever turn into is people getting defensive over their own choices or people telling people that their own experience of something (such as being an only child or finding parenting more than one child is easier) is wrong despite not knowing anything about the posters life.
The answer to this is it's entirely individual. There are some parents who DO find it easier parenting one. They maybe feel more laid back, less anxious and less pressured and if that's their experience then it really isn't for anyone to argue with or challenge unless you actually know the poster on a personal level. Similarly other people are glad to have stuck to have one and that shouldn't be challenged either.
The amount of children a person has and whether they find it easy is dependent on a number of things. The personality of children, the parents own bandwidth for parenting, support, finances and personal desires etc.
For me personally, I grew up with similarly age siblings and I have great memories of just playing with my siblings, the games we made up, the in-jokes we had. I didn't have poor social skills, I had plenty friends too who I'm still friends with to this day. But growing up with siblings added a dimension to my life that couldn't be replicated with friends or playing with a parent could have done. They made holidays better as we had ready made playmates, the games and memories you make with a sibling on holiday just can't be replicated with finding a friend. And many kids even with great social skills don't want to be forced to make friends on a holiday. And playing with my parents was never rhe same as playing with my siblings.
These were my reasons for having two based on my own experience. I wanted to give them what I had or a chance too. And of course it is a risk but everything is a risk whether you have one or 5 child.
And of course before people come at me, I don't think only children are lonely etc.