My first thought this morning, although a bit off the present research, concerns the 5 sons of Richard David of Strygos. (Will 1727)
We know that 2 of his sons, David and Thomas, had sons named David and here we are again, looking for David, (the son of one of the remaining 3 sons). It wouldn't surprise me if all of the 5 had sons named David. Three out of five is statistically relevant and, later, in our search for the father of the Rev. David of Hyssington, we will have to have definite proof of which of the three was his father.
Another noticeable point is that the known sons of Richard David named their sons after themselves or their brothers. The Rev. David (Hyssington) named his son after his brother Thomas. Thomas named his son after his brother David, David named his son David after himself.
The only brother name that we see in the next generation is Edward. None of the children are named William or Lewis. This fact, coupled with a total lack of information about those two, suggests to me that we could be looking at Edward as being the missing father for Rev. David.
Speculation of course but it may help later on.