Instead of having encyclopedic knowledge of every feature, I think editor fluency is being really good at the few features you need such that the editor is no longer the bottleneck.

The few features you really need to know for VIM are mostly in `:help motion.txt`. Knowledge of other features is obviously helpful in actually editing text, but being able to navigate well should remove most of the bottlenecks, especially considering how most VIM commands take motion into account.