I get that ugly software diagrams are not fun to look at, but to me dressing them up is like adding curves to a line chart - yes it's visually appealing but it interferes with the data being conveyed.
Had to take Color Theory to get my BFA. We learned things like the "speed" of colors: yellow is the "fastest" and purple is the "slowest". Only a little yellow is needed to balance out a lot of purple. Same for balancing the other colors. You use these balances for guiding the eye (lots of yellow on a purple field).
When you keep this in mind, diagrams or not, then the output will be "pretty" (not jarring) and "informative" (guiding the eye to the most relevant info).
Most diagrams have not had that must thought put into them. They should look a little ugly because that implies it might not be right so look for errors.
Weirdly, prettiness is the bigger red flag for me wrt to error. I see that and feel like more attention was put into that than the underlying information.
Ugly, brutalistic, utilitarian stuff tends to imply a focus on correctness to me.
If that means creating an overview of the system architecture for new team members that uses pretty colours and multiple fonts and icons and shaded boxes but that helps them to understand the system more quickly and correctly than an overwhelming page of black-and-white text and arrows, the extra styling has done its job.
The fewer right angles, the better: I can just draw shapes and put them in roughly the right spots and it'll look fine.
The very first example: x -> y
I rendered the svg, and then loaded ONLY the svg into a browser window.
I then looked through the whole of the document and tried to find how to align the output... and couldn't find out how.
Since the linked instructional was diverging from real life results, I stopped using it. :(
If you know how to fix it or could update the directions to ensure reliable output to the directions... that would go a long way for visitors like myself :)
Edit: did a google search for "d2lang connection left to right" and ended up here: https://d2lang.com/tour/layouts/
which may be helpful to you for the question I surfaced as it isn't linked in your overview docs :)