But part of that is because many of the old isekai shows aren't regarded as such, because they existed before the term.
And, like you could say the same thing about Urban Fantasy being all about toxic relationships and sexism. There is a lot of urban fantasy that follows those tropes... but that doesn't mean that Urban Fantasy is DEFINED by those tropes, they are just common.
I already pointed that out - Isekai
doesn't have to be a bunch of sexist power-fantasy drivel about nothing - but just like most Urban Fantasy
is sexist, toxic-relationship stuff or just creepy in a bad way, most Isekai
is drivel.
And the same exact problem exists with Urban Fantasy recommendations - if you see an Urban Fantasy novel on a list of "good fantasy novels" (or equally, any fantasy novel which involves a female assassin in her teens through early twenties - they have a similar thing going on*), if you're an experienced fantasy reader, alarm bells, even sirens and flashing lights, should be going off for you, because there's an approximately 10% chance that is actually a good, genuinely interesting book with something to say, which is worth your time, and a 90% chance it's awful drivel that just happens to fit someone's fetish, and makes the porn-iest horn-iest Anne Rice novels look super-classy and cool..
Likewise with Isekai - if you see one on a list of good anime, there's a 5-10% chance it is good (towards the higher end if the main character is not a teen/twenties boy), and 90% chance it's awful pap/pablum/drivel that just happens to allow certain to turn off their brains and lather themselves in the gross, unoriginal and frankly interesting power fantasy it represents - and again I still haven't seen a single Isekai that had good fight scenes or animation even - that's like the minimum you could ask if you're going to make a power-fantasy-centric anime.
* = There are good novels which fit this description, but they are certainly outnumbered strongly by bad ones which lean hard into a few gross tropes, and so-called "BookTok" has made sure the terrible ones are successful and well-rated. BookTok in general has succeeded in promoting way more completely terrible writers who basically should have stuck to fan-fiction than it has in bringing forwards hidden gems.