I'm not a huge fan of the isekai genre, but that doesn't mean I hate it either; its ubiquity is what makes me wonder why people don't just make straight up fantasy anime.
Frieren for example would be terrible if Frieren was actually some random person from earth who got sent into her setting (or, as Frieren's whole thing is outliving her comrades, her purple haired protege was the isekai'd protagonist); I understand how the isekai nature of an anime can also affect the anime, for example a character who has modern world knowledge he applies in the setting, or modern world tech, but if he just becomes a part of it, and NOTHING from his real life has any impact on the setting....then what's the point?
Overlord for example (which I didn't enjoy to be honest; I googled if he ever faces a challenge and nope, entire series and he has zero things that can challenge him) would not have been affected if he was just some lich who woke up a thousand/hundred years later.
Konosuba benefits from the isekai genre in that the isekai elements keep being relevant throughout (Spoilers:
spoiler
for example that guy who chose to reincarnate into the world with a powerful sword that Kazuma stole, or Kazuma dying and Aqua's replacement reviving him repeatedly, or that the demon lords at some point realized all their most annoying hero enemies keep starting in this one town and so decide to attack it, or that ancient scientist who turns out to be have been an isekai'd hero who creates stuff inspired by stuff he was a fan of
Most isekai animes today just seem to be wish fulfillment harem animes, which are a problem on their own as well, but they're paired with being isekais too (if you're wondering why I didn't make a thread on wish fulfillment harem animes, it's cause by and large I avoid them like the plague).
There are some interesting POST isekai stories that I found fascinating, stories where the characters came back from the isekai world and had their powers with them; in one case some of the heroes become devastatingly powerful villains who destroy entire cities, in another case it's a comedy about some guy who comes back and....could have been funnier without the ecchi/SA nonsense happening throughout.
Animes like SAO (which I didn't find interesting beyond the first story) make the other world an entirely false world and never let you forget the characters are real people who can actually die in the real world (sort of an anti-isekai genre).
In general, if they're not going to benefit from being isekai....then just make them normal fantasy. So many good fantasy animes out there that would have been hurt by making the protagonist just an isekai'd character.
You do get some post-apocalyptic anime; Fist of the North Star is a classic. However, the apocalypse fetish trope isn’t really all that present in anime because the apocalypse has a different context in Japanese pop culture. There, the apocalypse inevitably ends up being a metaphor for the nukes getting dropped on Hiroshima and Nagasaki. So it ends up being a reflection of what Japanese society actually went through, whereas in the West it’s a half anxiety, half intrigue at the possibility of what could come.
A sentiment people who have no real reason to fear being invaded or seriously attacked by a powerful nation have the privilege of enjoying; I doubt Vietnamese, DPRK, Libyan, Iraqi or Afghan story tellers would ever feel that way; Russians who suffered horrifically because of the Nazis all recognize the danger of Nazism but they still enjoy stories like fallout because they know their country isn't seriously in danger of resembling something in fallout.
If you wrote a story about the end of the white race in America, chuds will NOT feel that intrigue because they've convinced themselves a white genocide is being perpetrated
Notice that Western apocalypse films tend to assign the apocalypse to things like zombies, unforeseen disasters, vague allusions to unexplained societal collapse, supernatural or magical events. Even during the Cold War, apocalypse media that assigned it to the USSR tended to have a MAD outcome rather than the US falling.
Although, it is awfully noteworthy that we get tons of alternate history media where the Nazis won WWII and conquered the US but practically none where the soviets won the Cold War and the US becomes an Eastern Bloc country.