Welcome to the Purism community.
All the opinions in your post are fair.
Clearly the number of hardware kill switches is a difficult design issue, a compromise between flexibility and usability, as well as acknowledging a physical constraint.
Apparently Purism has decided that there is no separate kill switch for the GPS or the sensors. If you kill Cellular + WiFi + mic/cam then you also kill GPS and the sensors. That at least partly addresses your concern.
I don’t believe that anything would be “a simple fix” this late in the development process.
Disabling the GPS is not as important in an open source environment, since you can verify that a hypothetical program is not behaving in the manner that you describe and/or you can change it so that it does not behave that way. Where you choose to run an untrusted application in a sandbox environment, the sandbox itself can manage access to the GPS, whether by outright denial or by allowing only fuzzy values or by rate limiting.
With an open source operating system, the operating system itself can mediate access to most if not all peripherals.
Use of the gyro as a quasi-microphone has been discussed before e.g. Librem 5 (and 11/12) may need gyroscope hardware kill switch and e.g. "Librem 5 & PureOS ridiculously insecure"