I have to wonder -- considering that H3 is apparently available as a C library -- how fast it would be to simply enrich the lon/lat data with H3 data using a simple Unix filter using that C library before even importing it anywhere.

(One also wonders if the column-based database doesn't "cheat" when doing operations of the type "make a new table by adding new columns", since it could in principle COW-reuse all the unchanged columns in memory on that 70-second query.)