Yes, I know that, Sebastian... Especially the filling and sanding dragged on endlessly for us too... But now we are almost about to move in... "Only" the laminate on the upper floor and the baseboards throughout the house are still missing...
That's why I deliberately stayed away from it. I was once involved in leveling an old building with Fermacell including puttying and sanding. Once and never again. Flush with the wall is off the table. No one knows their way around it, no one wants to make an offer. A pity.
I'm not surprised that some hesitate to offer flush doors. It is simply much more complicated than installing "normal" frames. It already depends on the millimeter. In addition, no one likes to pay the extra effort and thus the price.