Suppose MCAS isn't the CAUSE
Suppose MCAS isn't the CAUSE, but is also a VICTIM OF the root cause. If you feed MCAS defective inputs one result of that is that it will do what it was intended to do - it'll pitch down. Suppose whatever is mangling the MCAS inputs is also mangling the airspeed data displayed to the crew. In other words, the computing and indicating systems on the aircraft are displaying defective information which the crew and MCAS are acting upon. Troubleshooting MCAS in this situation won't get you much because MCAS isn't the CAUSE - it's an EFFECT of a fault elsewhere. I'd like to see the logic chain between the outdoor sensors and the displays and systems. I'll bet there are multiple computing boxes in that chain where defective air data can be produced *without detection* by the crew - or the MCAS.