What Utah giveth up, Nevada drinketh away

I'm laughing at the idea of you playing devil's advocate in a state of maximum suffering and still sticking to the line that's it's a good thing. Your argument has the same character of solipsism - you're going to have to make the right assumption about the existence of consciousness in other people to engage with reality in a meaningful way, but I can't disprove you of thinking you're the only locus of consciousness in the universe.

Harris's concept of a moral landscape relies on an axiomatic claim (as all sciences do) that the worst possible misery for everyone is bad, after which it follows neatly that we can make epistemological claims about morality using scientific evidence, because we can make objective claims about the misery of conscious creatures and its causes. If that's not a ground level assumption able to be taken as obvious, prima facia, I don't know what could possibly compel anyone to make a claim about, and I mean this literally, any detail about their conscious experience with more than 0% confidence. All hard sciences rely on assumptions, for example that a shared, observable physical reality exists. Without that claim there is no basis for pooled scientific knowledge, but it is self-evident despite the counter-claim being nonfalsifiable. Much like we assume, from the nature of our own consciousness, that reality exists and can be observed, we can assume that the maximum conscious misery, as evident through the nature of our own consciousness, is objectively bad.