Concrete light shaft corner broken in shell construction - retention justified?

The comparison with the scratch is a bit off here, because apparently the support for a grating is completely or partially broken. Whether you can repair that with some kind of miracle filler so that it can again bear a person walking on it, no idea. If someone breaks off a part of the brake disc or puts a dent in the driveshaft during production of a Porsche 911, then the part is replaced and not "repaired" with window putty and spit.

And whether a scratch on a 911 is really fixed with a Smart Repair or if the entire body part, if possible, is replaced, we’ll leave that open. Surely they do that with a Skoda, but customers have different expectations for a 911 and pay different prices.

By the way, it was not about demanding that the entire house be torn down and rebuilt because this concrete part is not in order. But the argument "Yes, I broke it, but I can't afford a replacement, so I'll botch it" doesn’t hold up. To stay with the car example, the person who caused the accident could say "Sure, I smashed your entire driver’s door, but pulling dents, filling, and painting at my friend’s place should be enough..." No, in this case I have the right to have my vehicle restored to the condition before the accident, and that means a new door as an original replacement part, with everything that entails, at a dealership of my choice.

I find a retention until the repair is carried out / the defect is corrected super sensible and would do that for any trade. Otherwise, you really run after it forever.

No, in this case I am entitled to have my vehicle restored to the condition before the accident, which means a new door as an original replacement part, with everything that goes with it, at a contract workshop of my choice.

Apart from the fact that the same is done with a 911 as with a Skoda (identical procedure, same group, just believe me), read again what the OP wrote:

We were told that the corner would be filled with a special material from the manufacturer, afterward you wouldn’t see anything anymore, and the function would not be impaired.

Apart from the fact that no one here has yet seen a picture or anything similar that could allow them to assess the real "damage," it reads to me as if the manufacturer is defining "original replacement parts" there. This is certainly not the first time something like this has happened...

A proportionate retention is of course always advisable.