I've found it pretty useful. I switched from DDG to Google a few years ago because the knowledge graph results were noticeably better. We only just got AI results here in Australia about a month ago, and so far I've just found even more answers have a correct top result where I don't need to go digging.
Disclaimer: I work at Google, but not on anything related to search. I use plenty of non-Google stuff in my personal life so while I am biased, I have every chance to not use their search.
Allow me a remark: there's a difference between knowledge GRAPHS that are used internally at Google and knowledge PANELS that are displayed publicly in search results.
→ Knowledge graphs: sophisticated, internal data structures.
→ Knowledge panels: visual representations of SOME of the data from knowledge graphs.
You were thinking of knowledge PANELS: curated and user-friendly subsets of the internal data! :)
Disclaimer: I work at Google, but not on anything related to search. I use plenty of non-Google stuff in my personal life so while I am biased, I have every chance to not use their search.