You describe a more efficient design. If sufficiently strong material is affordable and used, and safety is not a concern, yours is not necessarily a "better" design. A transparent panel wouldn't be entirely invisible, and the visual effect of the staircase would not be the same (or as striking).
IMO, both the cable supported and transparent beam versions would be nearly as striking.
Of course, this is all down to aesthetics and judgment about what the design should prioritize. The designs I describe can be just as strong, or stronger, and cheaper at the same time, with additional safety features.
EDIT: To clarify, in my designs, there would be only one cable running to the ceiling, attached to the landing. Alternatively, one could use a transparent column.
