Agreed as to all parties, although I would add at least Ethiopian Airlines. But the question, in my mind, is to what extent should each be held accountable?

Boeing: somewhat for their treatment of a backup system as "optional equipment". As I said earlier, if they felt the additional safety of multiple sensors justified offering them as option, they should have been included as standard. As I understand it, system redundancy is so much the norm in airliner design they probably wouldn't even have had to justify the cost of it to their customers.

The FAA: probably not so much. They didn't farm out certification to Boeing for this one type only. According to the reports I've heard, it's been SOP for years, maybe decades.

The pilots: In the case of Lion Air, somewhat leaning toward giving them a pass, since theirs was the first case to come to light. In the case of Ethiopian Airlines, definitely. Ultimately the pilots are the ones putting their lives and the lives of their passengers on the line. Not to oversimplify, but if you see something unfamiliar in an airplane you're going to be flying you might want to ask, "Oooo ! What does this button do?" And as I have stated, by the time of the second crash the potential danger was well-known even outside aviation circles. I used to skydive, and one of the Golden Rules was "never jump a parachute you didn't pack", the crux of which is that YOU are the one who may die and therefore the one ultimately responsible for making sure you know what's going on before you step out of the airplane. Or on it, for that matter. And the airline's safety officials should potentially be held more accountable than the pilots, since their only job is to ensure the safety of the passengers. They should be scouring every incident report for any equipment issue, and especially when it involves an aircraft type their airline uses.