If you want to do document editing, then neither vim nor Kate are editors that do that. They are for editing text. You can write markdown, if you like, and then use pandoc or other tools to convert that to a printable document. I always use LaTeX if I need a pretty output, but that also has somewhat of a steep learning curve.

What you gain is the ability to manipulate text very efficiently. It’s hard to describe, but it kind of feels like a lower overhead protocol of communicating to the computer what i want it to do to the text compared to “normal” editors. Again, if you only rarely write stuff, it might not be worth it, but it feels great

Depends on how much you write. At some point the efficiency gain is probably worth learning vim anyway, but Kate is a nice editor and does the job.

I just like vim, it feels nice.