A utility basement presupposes a utility.
You don’t need it.
Have them explain exactly why a basement now, and show the costs with and without a basement.
Oops......someone just added a basement to my shopping cart.
If it really becomes cost-neutral or nearly so, it also does not need any benefit. Even if a basement can be constructed cost-neutrally to the slab (personally I have my doubts) The floor plan no longer needs to be changed because the stairs are accessible and there is a benefit for the utility room. How will the outdoor area be? How will the garden access be? How will the terrace be? What other costs arise outside the house?