Not the parent, but I find function vs fat arrow to be similar to:

* def vs lambda in Python

* fn vs closures in Rust

* def vs anonymous functions in Elixir

Honestly, given how often I find myself using small, immediately-consumed functions when performing common filter/map/reduce operations I find fat arrows to be an extremely welcome addition. I feel that it spares a lot of excessive "function" keywords everywhere and gives you just a little more room to have more verbose variable names when you have to deal with things like enforced maximum line lengths...

I write JavaScript/Node everyday. In my experience one does not write code like this when working with a team or a project that will be handed off; the author(s) are trying to minimize file size with expressions that are as small as possible. This seems okay to me for a library where your API is simply a function wrapper.