So then what it is? Because otherwise it's a magical nothing-term to which everything lisp people like applies, but no criticism can ever reach it because "that's not really lisp, see it's different in this other implementation"

In my mind, it's 2 distinct criteria: interactivity and the manipulation of symbols (whether those are implemented as symbols or identifiers doesn't really matter). I don't know about Erlang, but from the admittedly little JS I've written, I believe it achieves both criteria, even if it's worse at them than a "proper" Lisp.