I worked at New Relic and focused specifically on improving page load performance for one of the products using our RUM data. Even after combining/parallelizing API calls then embedding the data into the page, I found there was still an average 3-6 second average page load cost using React vs an already rendered HTML page which was nearly instant. Not huge but frustrating to discover the constraint when it was my task to improve it and our company was trying to be an example of great performance.
If your page is taking 3-6 seconds to load, you are either doing something wrong, or not understanding where the problem is and blaming React incorrectly.
My React app is statically exported and cached by the browser. There is only a single graphql call that fetches all necessary data. Backend is my only bottleneck. Everything else happens in less than 10ms.
And yes it is entirely possible to shoot yourself in the foot with any language and any framework. Including React.
That depends heavily on the device and network being used for testing. In my experience 3-6 seconds isn't out of the question by any means for a decent sized react SPA loaded on an older device and mobile network.
That isn't necessarily specific to react, any client-side rendered framework will have issues. React tends to be noticeably worse in my comparisons though, and any client rendering is going to be worse than server rendering your HTML.
