Yes, that thread didn’t pop up in the related items at first but once this thread started rolling I noticed it linked (win for machine learning). I definitely share your sentiment regarding the mental load, as well as feeling overwhelmed by the seemingly open-ended task of selecting a function from all possible functions instead of getting the “narrowing context” effect I feel in Python.
This github issue and the related ones to it were also relevant.
Something that became clear to me during the discussion in this thread is the way that language syntax interacts with completion. In this way, I claim it is not just a question of tooling. It is also not, as suggested by one of the other responses to your thread, a OO vs functional paradigm shift as demonstrated by the highly functional proposals above.
For me, autocomplete is much more than just a convenience, and having good autocomplete is absolutely essential for any language designed for scripting and rapid prototyping. I appreciate the discussion about it here, it has helped me formalize the abstract properties necessary to be able to create a fluid autocomplete interface.