What's wrong with the Java dependency? There's even a single-binary Bazel executable[1] that brings its own embedded OpenJDK. My company is using Bazel and the Java dependency has never been an issue.
Even if you write custom rules, you use the Python-like Skylark language and never interact with Java code.
No, that's generated also, but is highly reusable whereas some people get along completely fine without Java (unless you make them pull it in for Bazel for Firefox).
Well, no. Reproducible builds are a security concern and a source base distro is highly optimizable and configurable. Just because you do not see the purpose does not mean one is absent.
Even if you write custom rules, you use the Python-like Skylark language and never interact with Java code.
[1]: https://github.com/bazelbuild/bazel/releases (the single-binary distribution is bazel-1.1.0-linux-x86_64, it's only 40MB).