Well, I expressed my opinions on C++ libraries in the first few paragraphs. None of the C++ libraries I looked at support PDF layers for example (and as a graphic designer, you need that when working with maps, as maps are separated into layers).

QTPDF (used in QGIS) supports it, but the output quality is sub-par when working with Illustrator, at least in my experience. This could be a bug in QGIS, yes. But I didn't want to invest time into something that would probably fail (if the QGIS team failed using it, I would probably do so, too).

Yep.

https://itextpdf.com

Yeah, I would have recommended Kotlin. Runs on the JVM, so benefits from the matureness of Java, but is a more modern, and better designed language. A reason to choose Rust over this is if you actually have reason to believe you will need some extra bare metal performance over a garbage collected language, or you will need multiple threads. From what I can tell, the author did not really have good reason to believe any of those things, they just wanted to stay clear of whatever was wrong with the software they used at work, which a JMV based solution should have done. I am glad it worked out for them though, and knowing Rust is a good asset to fall back on, whereas learning Kotlin should be pretty easy for them. Even so, I like that with Kotlin you can take advantage of the most mature IDE ever made InjelliJ IDEA. I think they would have completed their project faster with this. That being said, the program they ended up with sounds very fast and it probably is faster than if they wrote it in Kotlin. It was the "right" move in the sense that it seems to have worked out well for them. Was it the "best" move? Most moves are not, and they don't need to be. Whether or not Kotlin would have been better probably depends on if it was better to finish faster or have an even more blazingly fast program at the end. I don't think a Kotlin version would have been slow or had any of that wait for 30 seconds nonsense, but it probably would have been a little slower. Would that a "little slower" have mattered? It depends on who is using the program and how they are using it. It always feels nicer to have a program that feels like instantly responds to your every whim.

The concern was quality, too. Yes, I thought about Electron, hell I even made a prototype for that. But in the end quality counts (to me), not speed of development. I knew that I had lots of time on my hands (no investors or anything, just my own money).

I didn't have anything to lose. So if you have the chance to make it perfect (versus taking some off-the-shelf tool and possibly ending up with a PDF that isn't quite what you want), would you risk it?