I'd much rather work with a developer proficient with C, Java, JS, React, DDD and a deep knowledge of Unix than someone who has spent the majority of their time

I'd much rather work with a developer proficient with C, Java, JS, React, DDD and a deep knowledge of Unix than someone who has spent the majority of their time on JS, Backbone/Knockout/Angular/Ember/React/Vue/Mithril, Redux/MobX/Vuex and Grunt/Gulp/Brunch/Webpack. Knowing how a technology works is important. Knowing technologies needed to accomplish tasks to be done is important. Knowing seven different technologies that accomplish the same thing is at best a marginal benefit.