In my opinion, only API classes and SPI classes should be included.
Classes in .impl packages (and nested packages) should not appear in the javadoc so as to discourage using those, and to make the javadoc lighter. And clearer.
Of course it's a matter of opinion, and you may not share mine. But the fix is simple, so I'll just go forward and submit a PR. We can discuss the issue on the PR and we can always reject it.