The difference between physical and software controls is pretty straightforward. (Closed source) software controls are just asking politely. Physical controls are making it so.

Airplane mode doesn't actually turn everything off, and it's not a guarantee like a faraday cage is. There are instances of devices still actually transmitting "stuff" in airplane mode, or having airplane mode silently disabled. A faraday cage is absolute, assuming correctly constructed, in that it guarantees zero signal can get in AND out. There's no ambiguity (again, assuming correct construction).

Airplane mode doesn't turn off wifi or Bluetooth, though obviously you can do that in addition to airplane mode.

In theory, an APT-type implant could keep transmitting even when airplane mode is engaged. This is what Faraday enclosures purportedly defeat.

Certainty?