I agree, HTTP is much simpler. I’m not sure it was available in OwnTracks when I was first playing with MQTT, but it’s by far preferable now. Yes, all the recipes assume that /var/data/<whatever> is on some sort of shared storage, be that Ceph, NFS, or something else.
FWIW, I stopped using OwnTracks when the HomeAssistant Companion app for iOS got advanced enough to handle location-reporting. (So that I can trigger various automations depending on whether I’m home or not)
D