Some thoughts on this:
- I agree with: Devices DO go offline silently. In reality it happens.
- Why monitoring only a couple of devices and not all? Are there devices in your smart home where you do not care if they are online or not?
- Why looking to/checking devices just to detect, that they are fine? If the device is okay, then a check is a waste of time. I guess you are interested in offline devices and not in the ones which are online.
- The only entities which give you a real knowledge about the device status are sensors and binary sensors, since this are the entities which are updated by the device itself. Think about it.
This is my solution (just for info):
https://community.home-assistant.io/t/detecting-unresponsive-devices/658030/16