There are many reasons for doing the things the author did, but I highly doubt saving time is a valid reason. The amount of time spent on setting this up and learning these tools and optimizing the workflows and writing scripts will most likely be much more than any time saved (real or imagined).
It is a similar pitfall that developers step into when they optimize their code before profiling where the bottlenecks are at.
But of course you should still do all of this, because it is a lot of fun and Vim rocks.
> It is a similar pitfall that developers step into when they optimize their code before profiling where the bottlenecks are at.
Author here. For reference I've made 5 courses over the last 4 years and have written over a million words. I also have 200+ blog posts and have hundreds of thousands of lines of code written across a bunch of projects.
In other words, I hope I know what my bottlenecks are with my environment. It's not specifically editing text, but it is managing a shit load of words across many hundreds of files and also switching between projects.
With no real prior Vim knowledge (I looked at it once many years ago) it took a solid weekend, and when I say solid, I mean I spent 10 hours both days researching Vim features, watching tutorials, following along with tutorials and slowly introducing a couple of plugins I knew I wanted (based on exact problems I had).
That got me to the point where I had the environment mostly working with a decent enough config file. Then I spent days floundering around like an idiot while I hardcore failed to even do simple things like "move to the 2nd to last word in a sentence and then wrap the last 2 words to a new line". Doing that without arrow keys and no mouse almost killed me initially.
After about a week of immersing myself I got to the point where I didn't feel like I was completely destroyed by a foreign environment. During this week I wrote about 10,000 words and worked on a couple of freelance programming gigs.
In my opinion, it was worth the 20 hours of set up + 20ish hours of not being as productive to set me up for the next 5+ years.
Plus as you mentioned, a side effect is it happens to be a fun too. That's a win win!
https://github.com/vimwiki/vimwiki
Also, consider checking out this blog post that describes a somewhat similar journey to incorporating vim (and vimwiki) in one's workflows: