That is kinda dumb, y'know.
Are you going to tell me that all anime/manga/comics/movies/etc that don't actually feature world transfers are isekai as soon as they introduce elements that don't exist in our world?
Isekai at its core is going to another world that's fundamentally different from ours. Saying that the mere imagination of any world counts as isekai is too broad a categorization. In such a case, how would you differentiate between cyoa that feature actual world transfers from those that don't?
This is the same retardation that birthed "native isekai".