Yes, UA should switch to the A321., I believe the Max is doomed. I think we will see more cancellations, and if that happens Boeing could be force to stop production. I can't see building 4,000 of this design for service over the next 45 years.
The aircraft design is flawed, I just don't see it being fully fixed with software, redundant sensors, extra alerts, more training. What you are training pilots for is how to avoid a crash when the plane tends to stall. Boeing is in a tough spot, but at the end of the day, they are going to have to stop production.
It would only take one more crash to doom it.
Boeing and others are blaming untrained foreign pilots - I disagree. These planes are supposed to fly on autopilot. Weather in both cases was good, so no external issue.