My George Adams was b. Feb12, 1789 and his father William (Wilhelm) was b. ca 1762. Obviously your William would be in the same generation as my George. William is in the same generation as your David b. 1765. It is very possible they are brothers. It is possible the wathers name was William but it is impossible for my William to bt the father of your David.
The German naming convention does not dictate that a son cannot be named after the father or that the first grandchild should be named after the grandparent although many did follow that tradition it was not set in stone.
My Valentine Scheurer (Schirrar) named his son Valentine and in turn Valentine Jr. named one of his son's Valentine. Now was that after the father or grandparent? It was not Valentine the third as his middle name was Willis. It is suggested the first Valentine may be Johan Valentine but Valentine Jr had no name other than Valentine that has been recorded.
If there is one thing I have found out about the German naming convention is that nothing is set in stone especially the longer they were in America and influenced by the English
As a side note, my Hoffs are also known as DeHoff like your DeHavens.