AFAIK DS, unlike RAS, is available under any flight rules, which I suppose emphasises your point.
That's what I understood too. But the acceptance of a DS means that you are able to follow vectors from ATC which potentially bring you into IMC conditions. So you should only request/accept a DS if you have an IMC/IR and the aircraft is IFR rated and you are prepared to switch to instrument flight as and when required, or on a CAVOK day.