I don’t think question of identity is relevant to physicalism at all.
Suppose it’s impossible to invert qualia without changing something physical in the brain. It’s still currious which one of two people I’d be in “creating a perfect copy” experiment.
That’s a non sequitur. The fact that many #3 feel like #2 doesn’t imply that #2 effectively do not exist.
I don’t think this is true and you didn’t provide any evidence in favor of this statement. But lets for the sake of the argument assume that it’s true. So what? How does it changes anything? Even if #2 is extremely rare it’s still the best of both worlds and something that we all should aspire too, isn’t it?
If you apply your cynicism in a less motivated manner, the same reasoning that makes you think that absolute majority of people who think they are #2 are in fact #3, would make you think the same for #1 and #4. Being an actual truthseeker is hard, it requires constant vigilance, constant fight against enthropy. Naturally most people who think themselves to be truthseekers are not them, regardless how nice they are.
The fact that there are a lot of not nice people who are not event trying to be truth-seekers doesn’t really matter to the point I’m making here. Or are you talking about something else?