I don't contest that those sites feel laggy and clunky, whether by poor load time, poor UX/UI, or some larger dysfunction. However, I would offer that the usag

I don't contest that those sites feel laggy and clunky, whether by poor load time, poor UX/UI, or some larger dysfunction. However, I would offer that the usage of React is not so much the cause of poor performance but rather a step taken to remedy scale lag. Large apps like the one you mention are big behemoths that take months to adopt new architectures and patterns, but those activities are required to ensure the scalability of the infrastructure and product development. During the time those apps are not fully transitioned to React (and Redux, and isomorphic rendering, and a fully-featured API, and webpack, and a litany of other tools), they might feel half-baked or sluggish, because you may have a page loaded with server-side template rendering, but half of your components on the page are upgraded to React, and take a second to initialize. IMO, React is a tool that provides an appropriately rigorous rubric for component development and a structure for large-scale interplay of reusable/composable frontend components, which was required for it to have any viability for a large org like Facebook. A lot of web apps are on the long trek to avail that potential fully, but while they're in transition, the experience of those apps will be a little disjointed or degraded.