I really think you need to give up on this particular line of
reasoning. In particular, your examples make it clear you're aiming
this at data exchange, not documents. As such, there is no "better" as
far as flat or fat. Better is determined by the needs of the data
exchange partners and can vary by use case, network bandwidth, target
device and a host of other constraints that do not allow for the kind of
generalizations that you are trying to make. Rather, at best these
recommendations are useless and at best they will lead to broken designs
that do not fit any needs at all.
+1. The thing is, you always have to ask "better? better for *what
purpose*?" In your zeal to promote what you see as "simple", you have
been consistently overlooking the purpose. And purposes vary.