Using another framework in place of Angular in the MEAN stack

I have been learning Node, Express and Mongo recently and from what I have learned about Express, it appears to handle a lot of the responsibilities which go into a "web app" parsing of your data, setting your views and specifically routing. To me I don't see the point of Angular in the stack when you have Express.

A year or two ago I tried a "Hello World" project in Angular and something the only thing I remember (which was interesting) were the custom elements and the routes (which were annoying—I didn't understand at the time why the URLS looked strange and had those "#"'s).

Am I not being fair to Angular cause I was a newb in general? Can someone explain why Angular is important to the other technologies and therefore used in the stack?

Is it possible like Vue.js or Ember.js in place of Angular in the MEAN stack?