This discussion goes at 2 levels:
- The technical characteristics of the MCAS "box", IE the electronics and the software.
- The functional characteristics of the needed MCAS feature to overcome the prehistoric design limitations of the B737 airframe.
The MCAS tech worked as build.
The MCAS feature as a system, to overcome the prepped up prehistoric B737 airframe limitations, failed.
Why did this MCAS feature fail: Simply because Boeing intentionally compartmented the development groups working on the B737 MAX, where the communication between the compartments was under management control, preventing all items, that could screw up with the Boeing commercial goals/promises, getting (technically) investigated (investigated as a proper engineering company should do).
And the management control of the technical interactions (between the compartments as well as with the FAA) gave Boeing the opportunity to lie towards the FAA about everything that might screw up with the Boeing commercial goals/promises.
Preventing technical development groups to communicate with each other, saves a lot of money, though also creates suboptimal solutions. The individual tech systems worked OK, the collaboration of these tech systems failed, because the overall design was not valued on feasibility (at least not for the MCAS area).
Or so to say, the road to disaster was simply built into the Boeing organization, explicitly designed this way to avoid exceptional costs (B787/B777). Exceptional costs which rise, when engineers step out of their own compartment, to take care of a proper system level integration.
Oh, there are other ways to tackle these exceptional costs: Just take care for a proper overall design right from the start, with sub-system interactions recognized/defined in an early stage. But hey, that doesn't match with the idea to El Cheapo prep-up a prehistoric design airframe with Botox.