The manual trim works if you aren't going far beyond the Vne of the aircraft. In the Ethiopia airlines case at the end of the flight the IAS of the AC was 458-500 kts. The pilots never changed from takeoff power (94% N1, more or less balls to the wall as the MAX has a massive surfeit of thrust).
Also note that the MCAS does not operate with the flaps deployed. While MCAS is inferior in terms of implementation (single sensor input an willingness to push the AC further outside of its documented flight envelope which means its not taking in data available to the AC, eg, altitude, the various airspeeds, GPS, GPWS) it can be shut off with the flick of a switch. Its more or less there to keep high pitch angles suppressed after the flaps are pulled up.
While I am not defending Boeing in this case (I was ANTI-MAX before Lion air and wanted a clean sheet for both mid market and small jet market) the manual trim system will work if the plane isn't going 100-150 kts past Vne - forces that the control surfaces experience will become exponential - this is why AC manufacturers have a Vne and barber poles. I'm sure the stick shaker was causing panic (even with 8000+ hours the captain might have never experienced one) and simply looking at the barber poles would give a hint on the overspeed situation.
The MAX should not exist and the MCAS system is flawed - but the system does not work if the flaps are deployed. Which means that when MCAS starts acting up the trim cutout switches and hand flying the aircraft in the flight envelope is a perfectly valid option.
Aviate, navigate, communicate. I think that in this situation communication (between PIC/FO) could have been an issue.
Boeing has a "simulated" low tech AC (which if I got my way would have been clean-sheeted like a modernized A320) which relied on software in the latest rendition to keep up the facade. But neither of the aircraft (Lion, Ethiopia) was doomed to being a total loss. The horrible training of the crew for the new AC type plays a major role - the type-certification for the 737-200 is valid on a MAX8/MAX9/MAX10, but the training would be drastically different. The fact the training is tied to the type-certification is sad. The 737MAX simulators are STILL as of May 2019 not truly complete for simulating Lion or Ethiopia conditions.
Boeing screwed up. (#1 not making a clean sheet small jet, #2, not implementing MCAS sanely), Training could have bridged the gap but this was forgone for expediency. Pilots were not trained in the differences in the various types within a single type-certified AC. I do think if pilots in general were more accustomed to having to hand fly aircraft this rubbish MCAS system would not have been as lethal as implemented.
If the MAX ends up banned I would not be sad - I'm not happy that a type-certification has been recycled since the 1960s. However this is a much larger discussion and not necessarily saying what the MAX and MCAS is is unworkable - if the AC had been clean sheeted this type of garbage wouldnt be necessary. We have AC manfacturers buying Bombardier and Embraer to avoid type-certifications - its better to no innovate and buy other designs than to just re-design the AC! And this is in the day of CAD and much better simulations! How is it "too expensive" now to clean sheet when the simulation tools are a million times better than slide rule created AC like the 747 and the SR-71 were designed? Crazy.