Those who wish to retain their sanity and retain keyword integrity across years, even decades, and multiple applications, will avoid hierarchical keywords. Sooner or later your hard work will simply get blown up. You probably won’t notice for three or four months and it will be nigh impossible to clean up the mess.
If anyone wants to play in the deep end with hiearchical keywords, s/he should be using an application like PhotoMechanic which is dedicated to handling metadata and resolving metadata conflicts.
That said, I’ve come around to like the idea of metadata editing in PhotoLab (one work bench, like in the good old days of Aperture) but the caveat that the metadata is stored where it belongs in the .xmp sidecar in standard format in real time.
Good luck with the hierarchical keywords! I’d love to be proven wrong.