I believe the Lion Air investigators have made public that there was a 20 degree differential between the two AoA sensors even when they were sitting on the runway before flight. (I don't have a source easily accessible.)

That's almost like saying two compasses should agree while standing on the north pole. These sensors need airflow to operate and provide meaningful indication.

It was during taxi for takeoff: https://theaircurrent.com/aviation-safety/the-world-pulls-th...

Sure, but they maintained their twenty degree difference for the duration of the flight. That's why the one stick shaker started going off shortly after rotation, why autopilot wouldn't engage, and why MCAS was going nuts.

Is that necessarily true? Based on this article (https://www.flyingmag.com/how-it-works-angle-attack-indicato...) it seems like they should be accurate regardless.

Why should an AoA sensor require airflow? And if we are talking about airflow, we are talking about measuring pressur differentialsm right? How to do calculate an angle using a pressure differential?

It’s literally just a metal plate that rotates with the oncoming air.

Ok, makes sense.