There was an interesting programme on Chan 4 (UK TV) last night on this topic. Much was made of the 2 accidents but the interesting bits involved two 737 pilots, one American and one British, in a simulator and they were caught out by the action of MCAS. After the instructions re operating the trim cut out switches were added to the relevant instructions, they still failed to "save" the aircraft. The reason seems to have been due to their having operating the cut out switches too late. It was suggested that, for the cut out switches to be effective, they have to be operated within 4 seconds of the onset of the upset and they took a little longer. By the time they threw the switches, the aircraft was diving toward the ground so fast that manual efforts to recover by heaving on the yoke came to nothing. The aerodynamic force being exerted on the stabilizer was such that they were unable to overcome it.