STAAD give provision of Master Slave Command to consider rigidity of RCC slab for distribution of horizonal shear at any floor level, between moment resisting frames/columns/shearwalls.

I have noticed some Structural designer avoid using Master Slave command. Instead, they consider Iy value of Horizontal beams almost infinite. Thier argument is that, RCC slab rigidity in XZ plane is better simulated by making Iy value of beam infinite which i feel is an incorrect assumption. This is beacuse, in the frame analysis, the moments are absorbed by beams and columns dont share any moment due to horizontal loads. Thereby, even in a 28 Storey tower, the %age reinf. in columns of size 1000*450 and M40 grade RCC comes less than 0.8%. Such low column reinf requirement in desgin output appears to be solely due to considering infinite Iy value in RCC beams. Pls confirm my doubts n argument.