I will say however, since I got an iPad Pro, I been using an App called Notebook by Zoho
https://www.zoho.com/notebook/
I have to say, it simulates the paper experience enough with the pencil that I seem to get the same benefit. I really enjoy it and I can still sync my notes across devices and it supports simple text edits checklists inserting photos and links and other cool things. I have to say its pretty darn good and I seem to get the same focus experience using this as I do when I use actual paper.
Maybe its the fact that when you are writing like this its the slowdown effect?