To me, minification is just collapsing of white space and line breaks, it doesn’t touch the code otherwise. It’s trivial to unminimize code.
In regards to obfuscation, this means actually altering parts of the code for performance gains or sometimes security purposes. Depending on why/how the code was obfuscated, it can be very hard or impossible to read naturally.
Even without utilizing production build options, webpack may output code that reviewers find hard to read. They also don’t want you to bundle any third party libraries with your own code, because it’d be hard to read and would make verifying the integrity of those libraries difficult.
React can be used just fine without something like webpack, as can any library really. Webpack is primarily a module bundling tool (dealing with imports/exports that browsers don’t handle yet), that also has a lot of other neat plugins that can be used over tools like Gulp. Sure it’s used a ton in React, Vue, Angular, etc. but is by no means required.
Unless you are doing super crazy things or adding in lots of third party libraries, I wouldn’t sweat the file sizes. Do what you can of course, but don’t let it get in the way of creating something cool.