Professional installation of the bathtub in new construction

Hello, can anyone assess whether this bathtub, installed by a sanitary specialist on behalf of the construction company, has been installed correctly? I am surprised that different and broken stones were used, and right outside the front door there was still a pallet with new sand-lime bricks, of which four could have been used. Is this thin rubber layer sufficient to ensure sound insulation?

Unfortunately, the construction company also made the screed cutout arbitrarily; at the short end, the screed is under the bathtub, while at the long end it is too short. They are now trying to shift this responsibility to the tiler.

If the stones are embedded in screed to fix them, could/should this be left as is or must something be corrected? Would one still line behind the upcoming tiling with insulation wool (self-installed) or leave the cavity because it makes no difference?

Thank you very much!

Looks all fine to me. You won't see any of that later, none of it will collapse on you in any way. How far the screed goes also makes no difference. If you want to maximize sound insulation, then stick Hawaphon to the bottom of the tub and fill the cavity with a suitable material such as mineral wool. Don't use anything that could possibly mold.

Fits. Nothing visible later!

I would rather be puzzled as to why an electrical cable was laid directly under the bathtub....