the creation of people is a complex moral decision

True enough. But it seems to me that hesitation in such cases is usually because of uncertainty either about whether the new people would really have good lives or about their effect on others around them. In the scenarios I described, everyone involved gets a good life when ask their interactions with others are taken into account. So yeah, creating livres is complex, but I don't see that that invalidates my question at all.

preferences, not happiness

That happens to be my, er, preference too. I think I do think it's a nitpick; we can just take "10x happier" as a sort of shorthand for some corresponding statement about preferences.

designed to confuse the moral intuition

I promise I had absolutely no such intention. I took the levels higher than typical ones in our world to avoid distracting digressions about whether the typical life in our world is in fact better than nothing. (Note that this isn't the same question as whether it's worth continuing such a life once it's already in progress.)

Your example of a world half as happy as this seems like it has a similar but opposite problem: depending on what "half as happy" actually means, you might be describing a change that would be rejected by total utilitarianism as well as average. That's the problem I was trying to avoid.