To OP - You sound kinda like me. I went over to Ecco Pro when I started doing programming as the amount of information coming into my head was way too much and I needed something that had low overhead seamless moving and organization of data. I found A single panel outliner (like Ecco Pro, Omni outliner...) works great for my brain.

Every time I download a notetaking app to try a new system, I pray it has an single panel outlining feature but nope. I can't count the number of times I considered writing my own.

Now you have mentioned Notion, I checked and it has an outline mode built right in. Woo Woo!! The only thing left to sell me is Linux support which is my primary DT env.

Thanks for the post!