As for the (build-time) performance concerns, I think there's some work here. They have a _big app_. And if you're compiling a 220 page app in a single build, it's going to get slow. You'd have the same problem, though, with a native mobile app or a very large C++ app: at some point, you need folks focusing on the infrastructure bits part time. With a relatively small number of changes, they can probably make some big wins: adding build caching for local development, using an NPM proxy (to avoid downloading 600MB of deps over the public internet on every build), looking at alternative hot reload plugins, etc.
That's not to say React is without problems, but I think it's worth considering that _almost any_ technology of the scale of React is going to have drawbacks, especially if you don't have someone in-house who has really significant experience making it work well. Companies like Airbnb, Facebook, Uber, etc. all have whole teams ("JS Infra") dedicated to this stuff, in the same way there are teams like Ruby Infra, etc.