I think the bytes per texel of depth24plus-stencil8 could be 4 - 5 instead of the current 4 - 8.

On dx12 we use DXGI_FORMAT_R24G8_TYPELESS and its typed friends which are 4 bytes.
On vulkan we use D24_UNORM_S8_UINT/D32_SFLOAT_S8_UINT which are 4/5 bytes.
On metal we use Depth24Unorm_Stencil8/Depth32Float_Stencil8 which are 4/5 bytes.

There is this note on metal's MTLPixelFormatDepth32Float_Stencil8 format though.

When using this format, some Metal device objects allocate 64-bits per pixel.

But I think this happens transparently since I see no way to query the actual size of Depth32Float_Stencil8.