"So far we where told that MCAS was initially designed to work only at very low speeds"
Nope just the opposite - at near cruise at altitude and a steep bank ' windup' turn at edge of normal- extreme flight envelope
Go look up satguru stuff or seattle times
Thats why only .6 degrees change in stab was needed. But at low speeds, they needed more deflection- changed it by a factor of 4- never notified FAA re the 2.4 degree whack.