Thanks for the appreciation, Andrew. If you are just talking about the tech stacks; it is indeed safe to say that with the MERN stack, the idea is that React (and the corresponding libraries in the ecosystem to make it a "full" solution) is being used in place of Angular. There is a great tutorial on going about building a MERN app, without any boilerplate. Do check it out.
mern.io is a full blown boilerplate, a full stack solution, as you have put it; for building apps with the MERN stack. It indeed uses Redux, React-Router; and has boilerplate code for implementing server side rendering, hot-reloading for React components, internalisation support, etc... to get you started as quick as is possible without you worrying about the little details.