> With MCAS disabled, all power assistance for the stabilisation functions were also disabled. To achieve the trim adjustments, they had to execute a "roller coaster" where they dropped altitude to reduce the air pressure over the control surfaces and reduce the required force.
The reason they were going so fast is because the pilots didn't disable the auto-thruster (which they should have done at the same time they disabled the auto-pilot). If they had done so and were travelling at normal flight speed then they would have been able to manually trim the plane with MCAS switches off, no special manoeuvers required.
Boeing makes much of their claim that the pilots of Boeing's are pilots not bus drivers. But the reality seems to be rather different: the pilot pulling back on the stick with all his might does not cause an override to be signalled to the systems. The trim wheels are motorised so strongly that the pilot can't physically stop them with his hand. All those potential inputs where the pilot is telling the computer to do something different are being ignored.
And because of that, the pilot is tricked into thinking he needs to do some fancy manoeuver and his attention is diverted there, whereas all he needed was to be in control of the flight surfaces, be able to fly straight and level and he would have soon realised that the auto-thrusters had been left on.