> This is wrong - on mixed use paths, it is customary and proper to announce "on your left" when passing

This is neither customarily nor regulatory uniform. There are mixed-use trails near me where bells are required. There are some trails where most people use a bell, some trails where nobody uses a bell, and some where there is a mix.

In my personal experience, the ratio of bikes to pedestrians and the purpose of the trail greatly affects how people tend to handle this.