Earlier quoted context omitted.
I tried that 'jk' thing way back, and I seem to recall it introducing some lag. Like a few milliseconds so it could process and see if you were hitting the followup key. Just enough to be annoying.
The lag thing is due to this: If you type `j` in insert mode, it waits to see if there's a possible `k` following. That's the lag. There's a setting for how long it waits.
> set timeout timeoutlen=3000 ttimeoutlen=100