No, it’s not nonsense – this applies to almost every house, because the absolute majority will open towards the west/south and then it gets hot. Or is your house only facing north and invisible on the other sides?
And don’t take the word "Rollladen" too literally, but replace it with "external shading element."
The details certainly depend on nuances, but in the end, it probably makes about half a degree difference.
By the way, I only have KS blocks, paid a lot of attention to summer heat protection on the roof, have roof overhangs, and we have no glass front facing west/south.
Oh, and ugly external shading elements on the upper floor – absolutely terrible.
And yet it still gets warm in the place.