Running bazel outside of a bazel workspace is not a major use-case that needs to be fixed.
It still has a slow startup time, bazel just works around that by using a persistent daemon, so that it is relatively fast after as long as the daemon is running.
Do you encounter cache invalidation bugs with daemonization often? I've had pretty bad experiences with daemonized dev tools in the past.
If you try to run two Bazel invocations in parallel in the same workspace, one waits for the other to be done.
The sibling suggests this may still be an issue. I'm not surprised—cache invalidation is very difficult to solve, and conservative approximations like tearing down the whole process each time tend to be quite effective.