The excuse that the bathtub is only for the children is ridiculous.
An excuse is not really necessary; it should just be an explanation of why the bathtub was given such a position. We like to shower and do so every day; as adults, we bathe at most maybe 6-10 times a year. A nice shower is very important to us, and we see that better fulfilled in that position than below. In the draft from the developer (which basically comes from your draft), there is a dark shower, or, if the shower wall is made of glass, no space left for a heated towel rail. The passage width from the entrance is also narrower. Unfortunately, the bathtub loses to the shower here and has to give way. I know the distance between the washbasin and the wall behind well (10-15 cm even less) from the bathroom in my parents’ house. I have never noticed it negatively. Of course, I would prefer 2 meters of space but would have to make compromises in other areas that I don’t like. I can certainly understand the point about the light, so I wrote that I would like to work with glass if possible. I have noticed the following: If the shower rail is installed with a distance of 40 cm from the lower shower wall (I could imagine that 35 cm would also work well here; are there recommendations?), then the distance between the “center of the fixed water outlet” and the upper wall would be greater than 120 cm (about 130-135 cm). In my estimation, this would mean that a heated towel rail could be installed on the upper wall. If that is possible, then the lower shower wall could be made half-high as a fixed wall and above it with glass, and the right shower wall could be made entirely of glass. This would on the one hand address the problem of light entering the lower area and on the other hand there would be no fixed wall behind you when standing at the washbasin.