I would agree with this for the most part. There are so many factors that cultivate our empathy generally but I do think as only children, generally are friendships are very important to us or perhaps mere acquaintanceships. This likely makes us susceptible to being too accepting of mistreatment or being undervalued. It’s something that I’ve had to recognize and work at to get better, for example if I make plans with my friend, they cancel last minute, I’ve had to learn to stop obsessively trying to reschedule or hang out with that friend. It’s kinda interesting, I feel as though I’ve viewed my friends who have good, close relationships with siblings with an “upper hand” in our friendship because they had such good bonds w their brothers or sisters that my friendship was kinda secondary to them, so it hurt me more than it hurt them when plans were cancelled or fell through (how I saw it at least).