Why would it be useless? Boeing's update for the Max8 MCAS (to make the FAA happy), was to make the system validate the two values.

If there is a mismatch, the system outputs an error and MCAS will disable itself.

In fact, that is literally one of the requirements set by the FAA to begin flying the Max8 again

> FAA Airworthiness Directive approved design changes for each MAX aircraft, requiring input from two AoA sensors for MCAS activation, elimination of the system's ability to repeatedly activate, and allowing pilots to override the system if necessary.

You can signal an immediate, specific warning if they disagree.

Turn on the AOA sensor error idiot light