An Epistemological Conundrum Creative Soul: What the hell are you talking about?
What are the basic hypotheses that comprise your so called OWN theory of mind that are subject to empirical test? What specific "If, then" statements does your own theory of mind generate, the validity of which, as you claim, can be put to objective empirical experimental test?
By the way, Einstein was noted for the many thought experiments he did conduct such as, for example, trying to imagine what it would be like (what his subjective experience would be like) to ride on a beam of light? However, this didn't mean that the validity of what he imagined to be the case subjectively didn't need to be put to objective empirical verification.
Also, Schopenhauer didn't smoke cigars so he really wasn't trying to land one; and only dogmatic brains are dead, not just those in vats.
The fact of the matter is that no one (neither you, nor I) will ever have airtight empirical verification about whether, or not, Schopenhauer's or Sartre's epistemological theory is empirically valid. Why? Because, unfortunately, neither theory, no matter how beautiful and complex its insights, generates empirically testable hypotheses.
For example, try to provide an empirical, experimental test for the following hypotheses:
Schopenhauer: If the human will is absolutely free, then guilt attaches to the "esse" rather than to the "operari."
Sartre: If human Being-for-Itself is defined primarily by a Pre-Reflective Consciousness, then such a consciousness will always be devoid of an Ego.
With respect to your "rubbish" comment.
Descartes' "When and while I think, I must exist" is a thought-act, an intellectual performance, that is existentially consistent and existentially self-verifying only when it is performed by the meditator (you and I) in the first person, present tense mode. In this sense, it is unique. One must execute it in order to "see" its truth. There is nothing incoherent about this!