the more I think about it the more I believe that why waves hands The Modern Isekai Tropes (as exemplified most recently in the dialogue that appears in Forspoken) bother me so much is that they seem to signal a sort of irreverent carelessness of the work's own setting &/or lore.
Like, if the main character, meant to be some sort of newcomer to this place, sees no issue with mocking/goofing on the traditions of the world that they are a newcomer to, why the fuck should I, the audience, care about the world? I feel like I am being told "this does not matter, don't worry about it"
As you say, if none of the characters seem to be taking the narrative situation seriously, why should I as the viewer? Any comedic value once derived from talking casually in a dangerous situation is in the stable of dead horses by now.
S'why I've been drawn lately to melodramatic media like Kamen Rider Black Sun, Thunderbolt Fantasy, or Ace Combat, where characters say completely ridiculous shit with a completely straight face because in-context it is serious. I can still laugh and hoot and holler when they say "I wonder which path you would choose... when looking in Harling's Mirror..." because it is absolutely a doofy phrase that's somehow even sillier when you know what Harling's Mirror is, but they say it with some damn conviction.
(also yeah, i got problems with isekai too)
"Exiled from my former party for being a woman" by Kaeruda Ameko and Seto Ririura isn't quippy exactly, and it might not qualify as an isekai as the character isn't portrayed as a transplant, but it's definitely trying to satirize both specific patriarchal attitudes in modern Japan and also within a pseudo-historical context; the lead is intentionally relatable as a modern woman.
And the world is portrayed as something you wouldn't want to be invested in! It's shitty and for someone like our heroine it's designed to keep her down! Were I in her position I'd fight against it too!
And that's really the issue with this specific form of quippiness, to me. It exists as window dressing, not to make any larger point. As a result, it's grating. Quippy, even intentionally annoyingly quippy, characters can easily fit into the context of a video game (see Portal 2), but if they lack any sort of purpose or point beyond that, no depth in their personality, then they're just an extraneous nuisance, by definition/design.
