I think there’s a conceptual problem here in how people store information and take notes rather than a technological one to be solved by features.
It’s key to understand that extensive keyword tagging in PKM graphs is detrimental. Exactly the kind of keyword tagging that you use in databases lke Zotero to find stuff will completely ruin your PKM system (been there, done that 
).
Here is a discussions about that topic that I found extremely helpful: https://www.reddit.com/r/ObsidianMD/comments/n7m5gx/backlinks_vs_tags/
Key quote:
Extensive content-based tagging is a known anti-pattern because tags create a weak association at best between notes.
By using content-based tags you are making yourself feel that you are creating associations but you are still really shifting the burden to your future self to figure out why the notes are associated.
This becomes a significant problem when you have a larger corpus and your tag ontology begins growing beyond control.
That said, I’d totally vote for qualified semantic links in the form of something like [[qualifier::note]], e. g. [[because::tags only create a weak association between notes]] or [[parent::product management MOC]] Currently I am sometimes using qualifier tags (paired with tag-specific CSS for making them visually stand out) as a workaround. (Disadvantage: separate qualifier tags are not coupled with the referred note, just weakly associated by position.)
PS: tags already are hierarchical if you want to. Because tags and pages are equal in Logseq. That feature is already there.