I get your point, "biodegradable" is not necessarily indicating the end state, but I think it's generally a better idea than using previously sequestered carbon like oil (depending on the energy needed to produce useful goods, and the source of that energy). As a related example, anything made of wood is biodegradable, but if you then burn it, you're not really capturing any net carbon, although you are sequestering it for a period of time.