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).