Talking of bundle sizes, this isn't inherent to the React point being made here but it's arguably too easy to blow up what you're serving. A common example I like to reference is Moment[1] — unpacked size is 4MB, most of which is different locales. If you _don't_ want to bundle all of those with your project, you have to do extra work, instead of making locales opt-in. Perhaps slightly less used, but a more prominent example, a widely-used table component Ag-grid[2] is 25MB before being packed down. Instead of being served as a modular set of components, it's mostly a big blob with minimal separation of concerns.
The takeaway here is twofold: we need better tooling as well as better practices for how to use those tools. It's both an educational problem as well as a toolset issue. It is possible to build lean and fast pages, but it's currently considerably harder than building gargantuan monsters. I don't see the web bloat problem going away until the dynamic here is flipped — it should be easy to ship small bundles even with minimal experience.