Gotta disagree with all y'all('cept Rater202).

Spoiler: Me disagreeing with all y'all('cept Rater202)
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Steven wants his Mom to be perfect. When he learns that she's not a perfect hero, his immediate reaction is to try to turn her into a perfect monster. Resolution comes in the realization that she is instead a flawed person who loves him very much. Just like Greg(who can't be there for him 100% of the time, and who sometimes has to settle for getting the pizza without pepperoni).

Coming to grips with this can be hard for a lot of kids.

I also think it's interesting to note that Connie hasn't had this realization about her Mom yet. "She always answers her phone". Connie's worry, at heart, comes from the idea that her Mom isn't a regular person who can get stuck in traffic or lose a phone; if she's not answering it must be a result of a major catastrophe.