>>279675232people say native isekai because they mean "this work feels exactly like isekai but the plot is different". The reason it feels exactly like isekai is that they're both canned plots used by hobby writers on the same fanfic website, Narou.
It's absolutely retarded to bring up that like Slayers had the isekai plot, that has absolutely nothing to do with why people notice that "I got kicked from the adventuring party" naroushit feels like "reincarnated in another world" naroushit. It's just from the same fucking website culture and the same hobby writers. There was never any need to reference the plots.