It's funny. I honestly don't know if I was a spoiled child, though I do know I wasn't generally bratty because I have always had a deep streak of people pleasing. But I definitely know my SO wasn't spoilt at all and is a wonderful person. I think the "only children are spoilt" maxim, if it comes from anywhere besides general nastiness, comes from the fact that an only child gets all the parental attention available. But parents of an only child can still not provide enough attention for one child (I have known only children who were emotionally and materially neglected), and they can provide WAY too much of the wrong kinds of attention (one way to characterize my fun-filled childhood).

(Also why are people terrible. "Can we get this one safely born please," is the LEAST they deserved from you and I'm so sorry they burdened you with foolishness especially when you were already very busy on a cellular level.)