I can't define psychedelic but to me if it alters my perception or makes me me feel otherworldly it's a psychedelic. From weed to acid to MDMA to Dissociatives.
I think some may be struggling because they are answering the question "is ketamine a useful psychedelic."
Ketamine is being studied for depression (did they finish?) but it has downsides (addiction) not seen in other non-dissociative psychelics nearly as badly.
Also dissociatives don't really leave you with anything to pull out of the trip. Ya you might have done some astral exploration but the next day you're still there, can't remember much of it and didn't gain anything.