Yeah, it's not my favorite part either. We've made them mostly unnecessary by adding inline tables, but for heavy nesting of arrays of tables, you still need to use them, which is why I mentioned that there are still some weaknesses for large, complex config files. Hoping to make this better in 2.0.
In defense of double brackets, I first encountered TOML in pipenv[1], and just by experimenting found I could add another source. So they're reasonably obvious if you see them in an existing file.
