You are correct, there is another dimension that has to be factored in… move to a single server/hub or have multiple server/sub-server and hubs.
To my joke and reality ‘Life sucks and then we die.’
Yes, I struggled with bluetooth low energy for a month. Bottom line, it’s implementation on Linux SUCKS!!! I have a solution that seems to run for multiple months (hoping for years, which is what I expect from Unix/Linux) as a raspberry pi/linux collector ‘hub’, but was it hard, yes. But have a found a better sensor end device than the BLE units, NO. So in balance… are they Linux python solutions, yes, are there ESP32 solutions yes. But I can tell you, based on experience, Wifi and Zigbee temperature / humidity solutions SUCK SUCK!!! So I have a bluetooth with a raspberry pi in my mix, will it play out as a long term solution, TBD. But it filled a price/performance/quality gap that I was unable to fill with any other tech mentioned, so it was add it to my toolbox. Growing…
Sidewalk, I am not going to debate, yes a whole corporate / privacy issue. But, you did not mention LoRa, which seems to be a positive ‘pretty open’ technology that addressed the use cases I mentioned. Of which, bluetooth, wifi, zigbee, zwave (maybe??) cannot address. And if Amazon increases the universe of hardware for LoRo, by pushing their own proprietary software on top of the same hardware I can use for LoRa, should I complain?
Okay we can open the whole LTE, 4G, 5G can of SPAM now too 
Life sucks and then back to work integrating 