Thick upper floor slab or statically optimized floor plan?

Architect-1 plans the reinforced concrete intermediate ceiling with 30 cm and has a lot of freedom in the placement of the walls. Architect-2 calls this "letting the forces wander" and means that, for cost reasons, the load-bearing walls should be better planned and then managed with 22 cm of reinforced concrete. The construction supervisor calculates 260 sqm * 8 cm = 20 m3 (additional) reinforced concrete * 150 € (85 per m3 concrete plus steel) = 3000 € and no reason to adjust the floor plan. Of course, the final word lies with the structural engineer, and small wall shifts don’t hurt anyone. But I also tend not to compromise on the floor plan design over 3000 €. I look forward to your comments on this.

It is not really answerable this way because it depends on which compromises you have to make with the floor plan.

That's true, and how these compromises are evaluated is naturally my very individual matter. So I ask differently: Is the assumption correct that the planning freedom only costs me about €3000? Or is there anything else to consider (the total height of the building is not expected to be a building regulation issue)? Architect-2, for example, spoke of additional costs of around €15,000, but usually builds other types of buildings.

You certainly won't have complete planning freedom, but you can compensate for part of it with thicker ceilings. However, we don't know exactly what you have in mind, so it's hard to judge. Basically, I find it more agreeable when you try to work with physics instead of throwing resources at a problem.

Is the assumption correct that the planning freedom only costs me about €3,000?

I agree with the opinion of
If you only build 8 x 8, €3,000 is wasted money for your "planning freedom."
If a room can only be 520 cm wide instead of 500 cm through this investment, I personally also find these €3,000 much too expensive.
We also had planning freedom without such an additional joker and live in a spacious open-plan room.

Basically, I find it more appealing when you try to work with physics instead of throwing resources at a problem

I agree with that too!

Architect-1 plans the reinforced concrete intermediate ceiling with 30 cm and has a lot of freedom in the placement of the walls. Architect-2 calls this "letting the forces walk around" and suggests that for cost reasons the load-bearing walls should be planned better and then 22 cm of reinforced concrete will suffice. Construction supervisor calculates 260 sqm * 8 cm = 20 m3 (additional) reinforced concrete * 150 € (85 per m3 concrete plus steel) = 3000 € and no reason to adjust the floor plan.

Is the assumption correct that the planning freedom only costs me about 3000 €? [...] Architect-2 spoke, for example, of additional costs around 15,000 €, but normally builds different buildings.

The latter does not "suffice" as an explanation for me. With a cost estimate disagreement of 5:1, I assume that the "truth" will be closer to the higher value.

Basically, I find it more sympathetic if one tries to work with physics instead of throwing resources at a problem.

I fundamentally consider "brute force" worth being "Plan Z". Between the Neanderthal and today, several millennia of humanism should lie (and should not have been for nothing).

But we don’t know exactly what you intend to do, so it’s hard to assess.

That could be remedied, after all, why do we have the good old classic external PM ...