So you don't even need to map ESC on tap (I prefer to map layout switching to it).
- Ctrl-[ is a chord that you have to press with 4/5 fingers using both hands at once.
- Whereas jk/fd etc are next to each other on the home row and pressed with 2/3 of the same hand sequentially.
Given the number of times you would have to exit insert mode, the second option is arguably more ergonomic...
So you don't even need to map ESC on tap (I prefer to map layout switching to it).