I wanted to share some work I have done to look at the community's tag set and estimate a hierarchy: https://www.cems.uwe.ac.uk/~pmatthew/blog/2020/06/19/a-ux-hierarchy-from-folksonomy/
A Vizualisation of top tags is here: https://fetstudy.uwe.ac.uk/~pmatthew/ko/ux-tag-viz.html
As you can see, the algorithm has put website-design at the top, though it looks to me like it should instead be usability, with forms and website-design under that.
I'd be really interested in your views, and if you think a hierarchy adds any value