The whole cave parable is like "what if the reality I experience is but a crude approximation and ill defined shadows cast by the real world? And I am forced to sit and observe reality this way."

This basically sounds like a description of when I am really drunk and my vision is blurring and doubling before blacking out (which itself proves impermanence and subjectivity of reality, if you think about it).

I think Plato was an alcoholic trying to dress things up in a baroque philosophical framework to justify it.