That's a good point, but people do need to keep in mind that many engineered systems with three points of reference have three identical points of reference. That's why it works so well, a common frame of reference (i.e. you can compare via simple voting).

For example jet aircraft commonly have three pitot static tubes, and you can just compare/contrast the data to look for the outlier. It works, and it works well.

If you tried to do that with e.g. LIDAR, vision, and radar with no common point of reference, solving for trust/resolving disagreements is an incredibly difficult technical challenge. Other variations (e.g. two vision + one LIDAR), does not really make it much easier either.

Tie-breaking during sensor fusion is a billion+ dollar problem, and will always be.