It's not just Isekai being akin to DQ lore wise. A constant in Isekai is that the characters are ALL some kind of Mary Sue and are OP in their new world.Because Isekai has elements of Dragon Quest which is plenty known in the country and a setting with plenty of fantasy that doesn't need to be explained, along established tropes that can auxiliate an author in trying to tell his story. And well, like any other genre, there's bad, good, mediocre and great Isekai.
It's funny/interesting once or twice but it's become grating that the entire genre is now "IRL loser gets teleported to another fantasy rpg world with a new game + save and is basically OP and gets all the chicks".
Really I can't think of an Isekai where the protag isn't OP/doesn't get OP really fast
(Except KonoSuba but it's like parody)