It’s definitely very childish and, imo, its meant to be. Amethyst’s behavior in “Maximum Capacity” is very much like a child acting out, wanting attention (even for a good reason), and throwing a fit when they don’t get it
A lot of people do this, it can be difficult to see things from another person’s perspective, so we often see other people’s actions in how it affects us and sometimes we’re blind to the other motivations. We’re closer to our own feelings so when we feel hurt we tend to not think about how other people are feeling or how our actions affect other people.
Amethyst feels hurt, she feels lonely, she wants attention and having difficulty empathizing and acknowledge the emotions of others (a problem I think all the Gems have), all she can think about is how hurt she is. Which is very childish, yes.