So what you're saying is that keyless start mechanisms (also wireless btw) in modern cars today are also poor design?
Even if the keyfobs on the S/X run out of battery, they can still be used to unlock and start the car. Just like the keycard on the Model 3 (NFC based no battery needed): https://youtu.be/0J1VbeDfQmg?t=24
Most keyless start systems have a backup physical key[1] hidden inside the remote fob and will use very short range RFID [2] similar to older physical turn keys and their immobiliser chips to authenticate with the car ECU and allow the engine to start.
I'm aware of this as I have owned cars with this feature. Modern cars do not use the physical key to "start". It's mostly only to open the driver side door.
Even if the keyfobs on the S/X run out of battery, they can still be used to unlock and start the car. Just like the keycard on the Model 3 (NFC based no battery needed): https://youtu.be/0J1VbeDfQmg?t=24