I agree. That is a very practical problem with Gnosticism. But it’s not really a theological problem with it. Secret knowledge is real, at least according to even mainstream scripture. Which means that the problem with Catholicism/Orthodoxy, which rejects this fact, is that it’s outright wrong.
I guess it’s a pick your poison scenario: do you prefer to be in an ambiguous position where you have to at least attempt to suss out who is authentically hearing the Spirit’s instructions and who is full of shit, or do you prefer to be just outright wrong?