You can still write simple apps by just putting in a script tag, that never stopped working. However, if you want to write a complicated app, then you've already accepted that you need complexity and thus you should be taking the time to evaluate different build systems, pick the right one, and settle on it. Like I said, there are multiple mature solutions to do that.

The fundemental problem is that you are either trying to write Hello Worlds with enterprise-grade build tools or that you're trying to write web apps with single script tags. Your hello world with React + Babel + Webpack is going to be big. That's the point, you're importing an library that is built to make extremely large complex web apps simple to make, therefore by definition that library has to be big and complex. But the joy is that you can then build out an entire web page with significant reactive functionality in a matter of hours.

I get that looking at a lot of options makes things look scary, but you only need to look at those options once you're ready to build something big. And big is going to be scary regardless. Until then, you will have no issues just importing a script into your web page for the little things.