When 105 mm guns suffice against destroyers

Would 105 mm guns alone give German capital ships enough anti-destroyer firepower?

Yes for the First World War, but probably not from the Second World War onward.

A 105 mm battery was adequate for anti-destroyer work on German capital ships in the First World War. By the Second World War, larger and more capable destroyers make the same battery much less convincing, showing how a weapon fit has to be judged against its period's threats.