300 sqm is in my eyes clearly a planning error
NO! Oh God, preserve us! You are talking about taste, which has nothing to do with planning. Whoever wants to build as many sqm as they want should do so. If he needs 60 sqm of space where another only needs 20, THEN THAT'S HOW IT IS. It's a matter of taste! If someone wants 20 sqm children's rooms and later wants to convert them into ironing and hobby rooms, THEN THAT'S HOW IT IS. It's a matter of taste! But if someone plans windows according to DIN, but they are covered with an overlay so that only a quarter of the lumens enter the room and the room finds no balance, then that is a planning error, because the room does not get the lighting it needs. My goodness, let's sort everything out a bit!