When there's a book that shows Diana imagining Steve Trevor's death over and over again or Black Canary imagining Green Arrow's death over and over again where Green Arrow and Steve Trevor are presented as helpless in the same way we see Lois in this book we can have that discussion. But the fact that it's a hypothetical now when you can point to decades of the reverse really should answer your question for you.
The expectations are not outdated when they explicitly want these marketed to people who see the characters on TV and in the movies and Superman and Batman are cross marketed to every age group imaginable. Man of Steel is PG-13, but Justice League Action isn't. Neither is JLU. I don't understand how this is a difficult concept. WHen you dress a book up like a saturday morning cartoon it shouldn't contain something as graphic and disturbing as this story. Yes parents have a responsibility to look at what their kids consume. I sure did and my kid won't be seeing this issue for a long time. But that doesn't excuse the fact that there are no ratings where people would expect them and the trade dress is friendly colorful and in this case a 180 degree contrast to the content.
And yes, people have come to rely on ratings and trade dress to give a shortcut to content. That's reality. Like the reality of not reading a 100 page comic in a checkout line designed to be for quick short trips.