It loosely reminds everyone of everything because “other planes of existence” is an all-encompassing meaningless term.

Just about every religion or fiction fits this, because they can–and do-- say “oh but it’s in oThEr pLaNeS oF eXiStEnCe!”. Which is a silly excuse because just about only concrete property that “other plane of existence” implies is that things on beings on it can’t affect things or beings on this plane of existence, so any theory (as in “has to make useful, verifiable predictions”) involving interactions between planes of existence is kind of dead on arrival.