Would you consider a world of 28 billion people living on rice an improvement?

It depends on a lot of other factors. More people living good lives seems like an improvement to me, all else being equal. I think it would be worth giving up richness and variety in food in order to facilitate this, though obviously that one aspect would be regrettable.

Why do you ask? What are you getting at?

I'm trying to see where your morality is coming from. It looks like 'assign a real value to every (multicellular) living creature according to how much fun it's having, add all the values up, and bigger is better'.

Whereas I greatly prefer 'A few people living in luxury in a beautiful vast wilderness' to 'Countless millions living on rice in a world where everything you see is a human creation'. I don't have a theory to explain why. I just do.

I'm sure that that's my evolved animal nature speaking about 'where is the best place to set up home'. And probably I'm dutchbookable, and maybe by your lights I'm evil.

But it seems odd to try to come up with new desires according to a theory. I'd rather go with the desires I've already got.