If your threat model includes airplane mode not working as intended, you probably shouldn't carry a phone at all.

May be but corporate greed for data surveillance occasionally surpasses the needs of state actors so much that they'll voluntarily invent features on the same level.

Google/Apple can in the future announce a "safety" feature that periodically announce Airtag'ish Bluetooth beacons even when in Airplane or powered off mode.

Comes down to the model of trust as much as any threat model. I don't need to perceive or even conceive of a specific threat to want to safeguard my privacy, even aggressively if I so desire.