I don't recall it not working. Though I don't use menus very often as I prefer making them manually.
Though if you say it's broken, it's worth fixing instead of just saying it's broken.
I didn't say it's broken, I just asked if I was wrong in thinking it doesn't work properly with sub menus, and if i should be doing something differently. Happy to try and fix it once I know it's broken and it's not just me using it incorrectly.
Then the slug is there if You call homepage route, because its set it up as a homepage if you dont want it you can use it as an internal link menutype, I think it solves your problem or extend your menupresenter with default home menuitem as you prefer.
I see where you are coming from, but relying on something that actually is available for your installation (version) will be most predictable, documentation as it usually is on open-source projects sometimes lack constant updates.
Being said that as I noted the open source, everybody can freely make a pull request with changes they would like to see in it.
Link to documentation repository