Frontend framework change

We are a small company, using emberjs as the main frontend framework for our projects. The frontend architect sticks to it like liquid glue sticks to paper, because he doesn't know any other frameworks. The main reason that is forced is the slogan: 'convention over configuration'. And there are reasons like emberjs is faster in larger scale applications. Anyone can reason pro-contra for emberjs, angular, react etc.. (hopefully someone who knows all of them, at least emberjs, and another)? We are having meeting sessions about this, where junior frontend devs try to convince the architect about the other frameworks. In my opinion this should not be a technical issue, all of the frameworks are capable of developing 'larger scale' applications. The real reason should be the recruiting, we would find react/angular devs more easily. Thanks