I feel that it’s a different type of simplicity: Denote is simple and well-designed, but I personally found it a hassle to actually organize things in it. For instance, to actually find again my content when I need it, I find that it’s important to design a good set of tags and actively apply them. Howm is more designed around making it as hassle-free as possible to input notes, and then let the notes surface in a “self-organizing” way. For instance, it’s easy to discover “sibling notes” that link to the same thing as this one (just click any link in the current note and all siblings pop up in a search buffer, below the note that you’re actually linking to).

Or you can use “comefrom links”, where you in some other file type “<<< foo bar”, and every time you mention “foo bar” in another note it becomes a magic link back to this spot. That serves kinda the same need as tags, but you don’t have to explicitly tag future notes or think about a system of tags, you just wrote normally and automatically get relevant links when you use consistent language. As a user, I feel this is much simpler to use, even though you’re right that Denote itself is implemented in a simple way.

Regarding the GTD system, I’ve also just ignored it ;). If I want a digital GTD I have had a great experience using Org, but these days I prefer a physical bullet journal as it seems to help me ignore unimportant tasks (I’ve always struggled with deleting unimportant tasks - not for technical reasons but for irrational reasons). And since it’s always in front of me on the desk, it’s harder to ignore than the agenda buffer.