Yes. You can have reasonable load times using JS with no bundler. There are some notes though:
- JSX isn't JavaScript, you will need to process these files (note: You can write React fairly reasonably without JSX).
- TypeScript won't work because it isn't JavaScript. I would only want to use raw JavaScript on the most basic of projects.
- A bundler/compressor is still going to reduce load times. Especially if you like lots of small files.
- Caching will be a nightmare if you aren't doing version-based naming.