For organizations, finding and governing content is critical to improve productivity. Content metadata—also called properties, attributes, columns, terms or tags—is essential for information archite...
I'd like to share briefly what I've done to move on from this issue in case it benefits anyone else. I'm somewhat new to SharePoint administration and development - so bare with me if implementing this sort of customization is common sense.
With the MMD filtering being such a poor UI experience for anyone using term paths as opposed to single terms (see my above post for an example), and with no acknowledgment (that I'm aware of) of this being an issue, I decided the best thing I could do is learn how to work with SPFX and customize our experience.
If you're unfamiliar with SPFX, a google search can get you started on setting up a dev environment and creating your first webpart.
Some kind folks have made some really nice controls on pnp.GitHub.io. I used their https://pnp.github.io/sp-dev-fx-controls-react/controls/TaxonomyPicker/to create a web part that lets you choose Taxonomy terms in a tree view or by text search. I then followed https://www.mavention.nl/blogs-cat/sharing-data-between-spfx-web-parts/ to share my selected terms with another webpart that displays the library and filters by the selected terms.
My second web part implements a datatable from datatables.net, I believe I followed this guide: https://www.c-sharpcorner.com/article/display-sharepoint-list-data-with-jquery-datatable-in-sharepoint-frameworkspfx/. My intention was to display the document library in a very clean fashion that's easy to filter. I added a filter row to the top of my datatable and implemented a receiver (from guide linked above) that would get the data from my TaxonomyPicker webpart and filter my MMD column appropriately. Datatables.net had plenty of information on how to customize the table.
It took me a couple of days to figure it all out and have the webparts working properly, but the UI experience for our customers (read only users) is vastly improved now with our use case. Below is an image of what the page looks like with the two web parts. I was also pleased that without any mobile-specific customization the page works really well.
I don't really mean to create a guide here - but I'm happy if this helps anyone else to continue using MMD in the way they need to without compromising on user experience.