On the flipside, you raise a very good point and I almost addressed that in my post as well, but I didn't want to get too long winded.
There does seem to have been a huge downward swing in quality of writing in media over the last ten years, this affects not only long running things but more recent things as well, so I don't know.
The rise of Identity Politics explains it somewhat, but I think a large part of it has to do with the quality of the writers' experiences.
60 years ago, most writers were war veterans - people who traveled the world far and wide or had a large circle of friends and family who did. These were men who fought in actual battles, read a wide variety of classic books, and had attended college back when it taught useful facts and required rigorous discipline.
40 years ago, writers were less likely to have personally fought in wars (unless they were old/young enough to go to Vietnam,) but they'd had family members who'd been in combat. They also grew up watching war movies. Even if they were total hippies, they could still roughly tell you how power structures and authority worked, and could competently plot out a battle. (They'd read lots of Heinlein in their youth.) They knew that cavalry was mobile, and not something you throw headlong at the enemy first thing. College was still a place where you could pick up useful facts and useful skills as a writer.
20-30 years ago, writers traveled less and were less worldwise, but had watched lots of old media growing up. The rise of the internet lead to communities of people who discussed media and literature, and created a place where aspiring writers could exchange and criticize each other's work. Online communities based around fanfiction began to spring up and tropes from Anime and other world media began making their way into Western culture. Feminism was just starting to rear it's head, thanks to shows like Buffy the Vampire Slayer, although women were still allowed to be pretty and sexy and men were still allowed to be strong and competent. Online fandoms were cropping up, but it rarely went beyond message board discussions, shrines to one's favorite characters and an annual trip to the local fandom convention (which probably took about 8-9 hours to get to if you lived outside of a major city.)
Now: Older writers are dying off en masse, and the fanfic writers who cut their teeth on anime and MLP fanfics are are all grown up and taking their place. Writers are chosen more for what politics they espouse than for their skill at writing. They barely have any life experience to think of, apart from their college trip to Mexico (which they spent hunched over their smartphone, tweeting,) and their SJW activism. Most of their greatest battles were spent attacking "racistsexisthomophobz" on Twitter and Reddit. Most of their relationships are narcissistic shitshows which will somehow find a way into their writing. (You can expect a show written in the modern era to become a therapy couch trip for the writers, because most of them are solipsistic and would rather write something that resonates with
their experience than write something that's of interest to anyone else.) Writers are more concerned with Representation and Diversity than story and plot. Writers are more concerned with pandering to the toxic elements of their show's fanbase than with writing realistic and nuanced characters. Orange Man BAD. White Man BAD. Only Women and POC Good. Everything is Political now and politics must be pushed at all costs otherwise DRUMPF WILL DESTROY US ALL!!!!
There are other factors afoot, but I think this goes a long way towards explaining the decline of writing in the post WW2 era...
