I've had precisely your reaction, and am stoked to share my enthusiasm for Roam (https://roamresearch.com) -- a graph-based system for codex / memex / personal knowledge-base / zettelkasten++
I checked out Roam (thanks for the rec!) and though I REALLY love the concept, I'm a little nervous to keep a massive interconnected knowledge base with a SaaS. Currently, I use Devonthink and though it's not perfect, I'm just so relieved I can have data on my machine with the storage system I choose. I miss the days of software storing data on my computer or where I want.
As a backend engineer, I just think: "Man, this data is just sitting in a db somewhere for any engineer to grep." Until we get to a point where everything is just encrypted by default, I just can't see myself trusting software like this.
I've recently started using Roam, and I'm really enjoying it so far. Probably the easiest information capture and reference tool I've used to date--it makes it very simple to get things down without slowing you down. Only major downside so far is no mobile app, but I know they are working on one.