For vim to become worth your time to learn to use effectively, you have to have a purpose to use it quite a lot. But it takes quite a lot of time, and causes quite a lot of errors in the mean time. Eventually, you are left with a skill and a tool that are a pleasure to use, but you literally must spend time actively learning how to use it. You cannot just pick it up, because you need to first memorize key combinations and the behavior of various modes. Then, you need to actually practice them.

And this proposed solution is even worse, because it suffers not only from the "vim effect", but from the "vim config effect", where you not only need to memorize, and practice, but actively configure your custom solution, which can take tons of time; is subject to loss/deletion; and is not universally available.

And god help me, what about programming? I honestly do not want to even think about multi-layered completions wreaking their havoc on everything I write, and the only alternative is different completions for different types of environments--even more cognitive load.

This seeks efficiency as represented by speed, but ignores efficiency as represented by ubiquity, generality, and low cognitive load.

If I want to get from point A to point B as quickly as possible, it is more efficient to run. If I want to get from point A to point B with the minimum energy expenditure, it is more efficient to walk. To be truly efficient, you need smart, balanced goals.