You bring up a good point, though, that "joy" isn't just the immediate work at hand, but also the entire context that you're in. I agree with that. Perhaps the argument about work alone, makes sense under the assumption that the larger context is also compatible with your values. If not, perhaps no specific activity will be joyous, and joining a different organization is the only solution?
So perhaps "joy" is still a valid thing to seek, but you're pointing out that it's more complex than just "do I like my current task?"