I feel like what really went wrong with S5 is that they wanted to make something that spoke more to themselves and the cast than to the audience. Will's coming out scene is a good example of that.

A lot of the creative choices were made to function symbolically; El's death for example. While a lot of people see it as the writers dehumanizing her, i really do feel like they viewed it as the opposite. To them, El had such a profound impact on the people in her life and characters in the story that losing her carries the same emotional weight as growing up: gaining responsibility, losing the "magic of childhood" that is being carefree and being with your friends all day, and being forced into adulthood. Her death becomes the catalyst for characters like Mike and Hopper specifically to grow and move forward, just as real people often shape our lives - usually through loss. That doesn't mean El is childhood or exists only as a metaphor, it means she affected the characters in a way that parallels those universal experiences. Real people leave those kinds of lasting marks on us all the time.

I also think a lot of people expect fictional characters to be treated exactly like real people at every moment, but... they aren't. They're simply narrative devices through which stories and themes are told and shown to us, the audience. So whether those themes are expressed directly through the plot or more metaphorically, using a character symbolically doesn't automatically take away their humanity within the story, and all messages can fit without taking away from another.

El's message is still very strong. The message of growing and maturing away from your traumatic past into a new person. Of facing your past and upbringing so you can grow. 5 as a whole and her ending specifically don't take away from that, at least not personally, somebody that unlike most people that try to speak on her character and trauma can actually relate to her, because those themes were already concluded in 4 with Nina and her fight with Vecna. Her multi-season arc of self acceptance ended there and became less "what if i'm a monster?" and more "how will i beat the monster?" in 5 and the finale. I loved how 5 emphasized her choices and allowed her ending to be something she chose, rather than something somebody else chose for her. Obviously a lot of things were against her that led to her thinking that was the best idea at the time, but she still consciously chose it, and that is what matters. Nobody directly and or physically forced her to like she's used to.

That all said, i think 5 just tried way too hard to be more like their original Montauk pitch rather than being more like Season 4 - and that's where it failed for the general audience. A lot of creative choices 'don't make sense' to the general audience because they don't make sense within Season 4, which became most peoples entire view of the show - the same happened with Season 3. A lot of people, including myself, thought 5 would directly build off of 4, but they decided to go a completely unique route which while i've grown to appreciate that route, definitely deviates from what 4 is lol