don't blame it on the airlines. Boing shouldn't have been able to certify a plane without redundant sensors.

Yes. But it wasn’t just about training the pilots, those systems/sensors should have been present even in the cheaper planes (or the cheaper planes simply shouldn’t have been sold).

It's worse because we literally did all this before. When the stick-shaker came out to help pilots know of impending stall conditions, the second one on the copilot's side was an optional extra! This despite the fact that the copilot is the Pilot Flying quite often in standard practice.

Do you have a reference for this? To my knowledge there was an optional AoA disagree indication (which was on a multi-function display so it's hard to argue it was any kind of cost saving). It's unlikely this would have been a factor in preventing either accident. A small warning indication with no actionable steps would have been low on the priority list for a pilot wrestling for control of the aircraft.