Somehow, from the information provided by the aircrew, the technicians were able to figure out that they had a malfunctioning AOA indicator -- which was replaced. The second one failed as well, for reasons that are not known (to us). So from a maintenance point of view, the reports were adequate.
Expecting line technicians in Ethiopia to discover a critical design flaw in a system that Boeing was keeping at least semi-secret is asking too much, in my opinion. Put yourself in the shoes even of a tech working in America, even if you had intimations that the shiny new 737 MAX was completely %$@!$ in rare circumstances and the entire fleet should immediately be grounded, would you pursue that line of inquiry? You have your 18 months of training from a vocational/tech school and you are going up against all of the PhDs at Boeing? I think not...