All true. Car manufacturers don't teach you how to drive either. Boeing and Airbus sell their planes and expect competent crew certified by their countries' authorities to fly them. All good, until it is not good enough. It would appear to be in the makers interest to hand hold at least some of their clients longer than others. There is a thought (not without grounds perhaps) that the Indonesian maintenance crew did not correctly identify or rectify the issues with the ill fated plane. But at least the flight crew of the Lion flight could not be blamed for not understanding what was happening. They could perhaps have been blamed for not being trained enough to GUESS or at least theorize the right thing to do especially when minutes or even seconds count. The Captain in hindsight (always 20/20) maybe should not have left his position and handed the controls to his Co pilot while he tried to find out what was happening. Perhaps at that particular juncture they should have been trying to keep the horse from bucking and doing their best to turn right around and land. Or perhaps it was already too late. But at that point in time no pilots knew about MCAS . What happened exactly on the Egyptian flight is not 100pct known as yet.
If I was Boeing I would want to (as part of my sales pitch) provide after sales supervision of the maintenance and observe and provide guidance for any flying issues for a time. Perhaps station some key personnel for a reasonable time. I don't think this is done now but it should be looked into.
Doesn't matter who crashes your product really. It is going to affect you.
p.s. I am not a Boeing fanboy though as I love Airbus products equally. I'm not fond of the sidestick though, where one pilot doesn't "see" what the other is doing.