I accept all of your premises but disagree with your argument -- yes the lack of an emergency alert system is a factor, yes cell phones have a built-in alert system that could have handled this, and yes Amazon chose to suppress this alert system from working by denying employees access to their devices. They took away the only existing alert system and didn't replace it with anything. Garden variety negligent behavior leading to deaths.
Its not an argument and we came to the same conclusion. The case needs to focus on the lack of emergency system instead of getting thrown out unceremoniously by a judge who says "whats this got to do with cell phones"