Even granting you all of your premises, everything we know about brains and qualia we know by observing it in this universe. If this universe is in fact a simulation, then what we know about brains and qualia is false. At the very most, your argument shows that we cannot create a simulation. It does not prove that we cannot be in a simulation, because we have no idea what the physics of the real world would be like.

Like pjeby, you're attacking a claim much stronger than the one I've asserted. I didn't claim we cannot be in a simulation. I claimed that if we are in a simulation, then the simulator must be of a sort that Bostrom's argument provides us no reason to suppose is likely to exist.

In general, John Searle has some serious problems when it comes to trying to answer essentially empirical questions with a priori reasoning.

There's nothing wrong with trying to answer empirical questions with deductive reasoning if your priors are well-grounded. Deductive logic allows me to reliably predict that a banjo will fall if I drop it, even if I have never before observed a falling banjo, because I start with the empirically-acquired prior that, in general, dropped objects fall.