Floor plan design single-family house, 600 sqm plot, 1.5 full floors

What is of course also unfortunate, I only see now that the exit from the stairs at the top is very tight against the wall. As mentioned before: without measurements, one can say little. One could mitigate the narrow spot if the door is located opposite the exit, so that ladders and the like can also be brought upstairs.

We are grateful for every suggestion.

Really? - then I'll make a radical one: back to square one!

Mix of standard drafts from the general contractor combined with our wishes (dormer + bay window)

That is probably exactly the diagnosis. I can well imagine that the majority of those involved for inspiration found pure standard drafts more convincing than the concocted Wolpertinger (just because you want a convertible with a large tailgate). Blueberry ice cream with dark chocolate mayonnaise. Such "mixtures" can lead to nothing more than diarrhea. Every attempt at improvement increases the number of corners and dissatisfaction. Straight, single-flight stairs are already a burden for the floor plan in an old town villa – here, it probably also added that the upper floor must not be a full story, hence the roof bulges. This struggle certainly won't be resolved with further contortions.