[sehr]

throw away MVC and replace with with a big ol' render() function that spits out "HTML"

Simply put, no. React.js can be treated as a simple, dumb view or part of something larger ala Backbone, Flux, etc..

Angular.js doesn't even have a model layer aside from $scope, which in my experience is being thrown away more and more in favor of controllerAs syntax & convoluted services masquerading as 'models'