I stumbled upon your very nice analysis while trying to understand how ‘useful’ the Helium network actually is. To elaborate on this, I think quite some of the real data packets are used for Coverage Mapping, which seems to be quite popular. It is promoted by the 10000 DC you get for free when creating a new account on the Helium Console. However, I would not call this a real use-case, as it purely for the benefit of the network itself (and maybe the fun). Also, I suspect people to buy DC when HNT is low, and then let a sensor transmit meaningless data to their own hotspot in case of more favorable HNT price.
On another note, with the upcoming Data-Only Hotspots, would it be possible to simultaneously connect them to TTN? If we could somehow encourage the miners to do this…