I define gibberish as "difficult to understand and entirely or almost entirely meaningless". I think Plotinus and Foucault are "difficult to understand and entirely or almost entirely false". A statement is meaningless if it either fails to follow rules of syntax, i.e. "Running the the snacks on quickly!" or semantics, i.e. "Green ideas sleep furiously."

The distinction is actually pretty important. If you know something is meaningless then you can move on, but you can't decide something is false without first considering the argument, obfuscated or not.

There is some middle ground when it comes to arguments about things that don't exist. The trinity argument (and probably Plotinus) appeals to something that doesn't exist and so it says things that would be meaningful if the holy trinity was real but can't really be evaluated since there is no such thing. Obviously there is no reason for you to care much about this argument. But I don't think Hegel, Foucault or Heidegger and the other usual suspects are talking about things that don't exist.