I'll often use Up/^p/^r(i-reverse-search) to find a previous command and edit it's argument, which is where the tree nature of this tool would come in handy. If I 'type' the first n terms of a command enough times, it might be better to alias that part of the command rather than navigate my history and then edit the rest of the command repeatedly.

Likely yes. He mentions that he turns off deduplication for the experiment.

You're right that it does not accurately describe his typing, but it does describe which commands he uses most... which is about half as good.

Better yet, just set your history to 10k-20k+ items and use reverse-search (ie. Ctrl+r in bash) to recall your old commands. Navigation aside, about 80-90% of commands I use regularly are already in the shell history.

If you want to keep your fingers on the home row, I find `ctrl p` to be more comfortable and faster.